Getting Started

To get started with VOSviewer, you may want to take a look at some of the sources of information listed below.


Share this page

VOSviewer manual

The VOSviewer manual provides detailed and up-to-date information on the functionality of VOSviewer. The manual can also be accessed using the Manual button in VOSviewer.

Open VOSviewer manual


VOSviewer book chapter

VOSviewer is discussed in detail in a recent book chapter. The chapter provides a tutorial in which the use of VOSviewer is demonstrated in a step-by-step manner. The chapter is based on VOSviewer version 1.5.5. Some of the improvements and extensions introduced in the most recent versions of VOSviewer are therefore not covered in the chapter. In addition to VOSviewer, the chapter also discusses the CitNetExplorer tool for visualizing and analyzing citation networks of publications.

Open VOSviewer book chapter

VOSviewer paper

VOSviewer was originally introduced in a paper published in Scientometrics in 2010. In the meantime, VOSviewer has been improved and extended in many ways, so the paper is not fully up-to-date anymore. However, it still provides a useful introduction into the main ideas underlying VOSviewer.

Open VOSviewer paper

AIDA bookletAIDA booklet

The AIDA booklet introduces diverse case studies on research positioning and trend identification. These case studies are relevant for PhD candidates, researchers, group leaders, and policy makers. Many of the case studies make use of VOSviewer.

Open AIDA booklet


Mandatory fields
  • Pablo Rodriguez December 8th, 2018 11:40 am
    Thanks a lot for this incredible tool! I just wanted to ask if is possible to export the items after clusters are generated, in the Items tab we can see for each cluster the items that conform them, is possible to export such list of items?
    Also similarly, when we create the map for example "create a map based on network data" then I select the map file and the network file, then I have to chose the total link strength of an item and at last there is a list of all items and their respective strengths, is possible to export or select or copy that list of items with their strenghts?
    Because I think it is important to show the strenght of each item as a measure of the "quality" of the item, if I understand it right the larger the strength the more important is the selected item.
    Thanks again for your great work
    Best regards
    • Ludo Waltman December 8th, 2018 12:28 pm
      When you save a map in a VOSviewer map file, the information that you are looking for can be found in this file. A map file is a plain text file with tab-delimited columns. It can best be opened using a spreadsheet program such as MS Excel.
  • giuseppe vito November 19th, 2018 10:25 am
    Dear Ludo, dear Philip H., I had encountered the problem having already worked uncheking FOUNDING DETAILS and "Tradenames & manufacturers" and "Accession numbers & chemicals" in the section OTHER INFORMATION. Uncheking in BIBLIOGRAPHIC INFORMATION everything except "Affiliations" and "EID", "Access Type" and "Author (s) s ID" in the section CITATION INFORMATION, everything works for the purpose of my work. The consistency remains in the fact that with the same restrictions on the export of metadata, some subsets of a research on Scopus that is treated by Vosviewer without problems, are not read by the program. I hope to have contributed to the issue, also suggesting something to the Scopus team. Best regards
  • giuseppe vito November 18th, 2018 6:05 pm
    Dear Ludo, here I am again:
    a csv file from Scopus obtained with the query (SRCTITLE (sustainability) AND AFFILCOUNTRY (italy)) AND (LIMIT-TO (DOCTYPE, "ar")) returns 900 refs. [of which 42 contain the keyword "climate change"] and Vosviewer treats it without problems.
    By limiting the search in these 900 docs to the exact keyword "climate change" with the query
    (SRCTITLE (sustainability) AND AFFILCOUNTRY (italy)) AND (LIMIT-TO (DOCTYPE, "ar")) AND (LIMIT-TO (EXACT KEYWORD, "Climate Change")) Scopus returns the csv file containing 42 refs but Vosviewer fails to read it by returning the error "... incorrect number of columns". The fact amazes me because this second file should be (is) a subset of the first. Can you kindly help me?
    • Ludo Waltman November 18th, 2018 6:35 pm
      This is indeed very strange, but I am afraid I cannot help with this. There currently is a problem with the Scopus CSV export. The nature of the problem is not entirely clear to me. The problem needs to be fixed by Elsevier's Scopus team. Hopefully they will do so as soon as possible. There is not much I can do at the moment.
      • giuseppe vito November 18th, 2018 6:48 pm
        Dear Ludo, thank you all the same, I'll try with Web of Science. Good Sunday evening
        • Philip H. November 18th, 2018 11:24 pm
          Please that the workaround offered previously by another contributor here DOES WORK. In the selections under CSV Export UNCHECK the box next to FUNDING DETAILS. Then try to export and upload.
          It has worked for me even after I ran into the same exact problem.
      • Maryam Mazaheri November 23rd, 2018 11:24 pm
        Ludo Waltman
        As i had the same problem with scopus, i try publish or perish software and the Csv. result File that the software get is shown in vosviewer.
  • Nikhil November 16th, 2018 12:50 pm
    Hello everyone, Can someone please clarify?
    When I create a co-citation(cited references) map, a particular node has following information:
    Item: graham Jr, 2005, i account econ
    cluster: 3
    links: 215
    total link strength: 739
    citations: 47
    If I understood correct this node has 215 links with different nodes in the map and the sum of strengths of all links is 739. But what is do this 215 links actually show? is it no of co-citations? if not how can I find no of co-citations?
    Thank you in Advance
    • Ludo Waltman November 16th, 2018 10:58 pm
      When you move the mouse over a co-citation link, you can see the strength of the link in the status bar. The strength of the link equals the number of co-citations of two cited references.
      • Philip H. November 17th, 2018 2:12 am
        Could you please clarify this point further concerning 'strength of links'.
        - I had thought that the lines 'linking' two nodes on a citation map (e.g., documents) were indications of the number of times a document had been CITED BY ANOTHER DOCUMENT.
        - I had thought that the proximity of two nodes were an indication of how frequently two documents had been co-cited.
        Based on these assumptions, I wrote in a ms. the following: "Density of 'links' connecting two scholars reflect the number of times a scholar has been co-cited by another scholar."
        I guess I am confused!
        Please reduce my confusion! :)
        • Ludo Waltman November 17th, 2018 9:18 am
          The proximity of two documents indeed is an indication of how frequently the documents have been co-cited. A link also represents the frequency of co-citation of two documents. It does not represent the number a times a document has been cited by another document. The expression 'co-cited by another scholar' should have been 'co-cited with another scholar'. I hope this offers some clarification!
          • Philip H. November 17th, 2018 11:17 am
            Therefore, 'denser links' between two scholars would indicate higher co-citation of their work by other scholars. Your explanation leads to 2 follow-up questions.
            1. If proximity of authors and the number of links between two authors BOTH reflect the degree of co-citation, then why are some authors with many links far away from each other on the map?
            2. Does any info provided in the map offer an indication of 'which scholars' are frequently co-citing other scholars?
            Thanks. Your prompt and clear feedback is really appreciated by all of us users of VOSviewer.
            • Ludo Waltman November 17th, 2018 12:30 pm
              1. There are two reasons for this. First, only two dimensions are available for the visualization. A high-dimensional data set therefore needs to be projected into two dimensions. This means that the data set cannot be represented in a perfectly accurate way. For this reason, strongly linked items are sometimes located far away from each other. Second, the distance between two items in fact indicates the strength of the relation between the items after normalizing for the fact that some items (e.g., authors with many publications) tend to have stronger relations than others (e.g., authors with just a few publications). The normalization is selected on the 'Analysis' tab in VOSviewer. The default normalization is the so-called association strength. It is also possible to turn off the normalization.
              2. No, this information is not provided. However, the map does show which authors are frequently co-cited with other authors. These are the authors with a high total link strength. They have a large size in the map, so they are prominently visible.
      • Nikhil November 17th, 2018 12:36 pm
        Thank you for your reply.
  • Pedro November 13th, 2018 6:22 pm
    Hey Waltman. How are you?
    I'm trying to use the VOSVIEWER for a survey paper. Nevertheless, I have a doubt about the Thesaurus file. Can you help me?
    So, as database papers, I send you this file from Scopus (it is a bit old and is not having problems as the recent files from Scopus database) . In this database, I have to replace some keywords, e.g. micro grids by microgrid; micro grid by microgrid, etc, as you can see in the file Thesaurus_1.
    On other hand, I have to standardize the name of an author: thorp, j by thorp, js, as you can see in the file thesaurus_authors.
    In both files, I think that I follow correctly your example of thesaurus files, however, when I try to generate the results, nothing happens. Can you point me where I'm wrong?
    Thank you in advance for your help, Mr. Waltman.
    I emailed you with my files.
    • Ludo Waltman November 13th, 2018 6:57 pm
      You need to use the Scopus format for author names (rather than the Web of Science format). This for instance means that 'thorp, js' should be 'thorp j.s.'. This should solve your problem. If it doesn't, then please let me know.
      • Pedro November 14th, 2018 1:22 am
        Thanks, Ludo!
        It is working now!!
  • Ana Paula Ermel November 13th, 2018 12:46 pm
    I having a problem successfully uploading a Scopus data file. When I downloaded the data file of the Scopus (CSV), and upload in Voswier, gives an error message of an incorrect number of columns in row 276.
    • Ludo Waltman November 13th, 2018 1:13 pm
      Unfortunately, there are currently problems with CSV files exported from Scopus. We are in contact with the Scopus team about this. They are investigating the issue. Hopefully, the problems will be fixed as soon as possible. As a workaround, you could consider using other data sources, such as Web of Science or Dimensions.
      • Ana Paula Ermel November 13th, 2018 1:49 pm
        Thanks, Ludo!
        I'll be waiting.
        • Ana Paula Ermel November 14th, 2018 12:56 am
          I just discovered that by unchecking the "Funding details" option when exporting the CSV file, VOSviewer runs it normally.
  • Oloiva Sousa November 11th, 2018 9:36 pm
  • Oloiva Sousa November 10th, 2018 8:38 pm
    i think that this application is excelent!
  • Philip November 10th, 2018 10:49 am
    One of my doctoral students is having a problem successfully uploading a scopus data file. Although she did not have a problem in the past, when she updated the data file in scopus and downloaded again, VV gives an error message of an incorrect number of columns in row 276. her old file is still ok.
    We've tried exporting a fresh csv file, renaming the file, deleting a record and saving under a new name etc, but no luck. Any suggestions?
    • Ludo Waltman November 10th, 2018 5:14 pm
      Could you please send your files to I will then take a look at your problem.
  • Angel Bravo October 31st, 2018 8:09 pm
    Hi, would you tell me where I can find the thesaurus_authors.txt archive please
    • Ludo Waltman November 1st, 2018 7:49 pm
      See the downloads available at
  • Philip Hallinger October 30th, 2018 1:47 am
    Hi: I understand that the overlay visualization in co-word analysis will reveal the 'research front' in the particular literature. I would assume that the research front for the current literature would be the last five or six years.
    1. Therefore, I don't understand why the default for a temporal overal in a review that extends from 1960 to 2018 only shows the research front for 2006-2014.
    2. Also when I try to adjust the years in the legend bar to be 2010 to 2018, all of the topics change to a darker color.
    What am I missing here?
    • Ludo Waltman October 30th, 2018 7:24 am
      The colors show the average publication year of the articles in which a particular term occurs. These averages typically are located somewhere in the middle of your time period. It is unlikely that a term occurs exclusively in early years or exclusively in very recent years. This is why there will be hardly any terms in your data that have for instance 1965 or 2016 as their average publication year. In the case of your data, most terms apparently have an average publication year between 2006 and 2014, and the color scale is automatically adjusted to this.
  • Ngan Kim Nguyen October 29th, 2018 12:07 pm
    Thank you so much for the useful and powerful tool for researchers.
    I have read the manual as well as watched some videos for instruction. However, I cannot find Information Panel even though I imitated almost the same steps from downloading data from Scopus to creating map for co-occurrence between terms. Any thing is alright except no Information Panel. I checked data on cvs file from Scopus, there is information of journals name. However, when I saved the map created by VOSviewer as map file, and checked that file, there is no Description column. I googled this case, but no information.
    I am very grateful if someone can instruct me what I should do to see the Information Panel.
    Best regards,
    • Ludo Waltman October 29th, 2018 12:22 pm
      The information panel is available only when you have created a map of documents. Maps of other types of items do not make use of the information panel.
  • Flavio October 20th, 2018 7:46 pm
    Dear all,
    I am performing on VOSviewer version 1.6.9 a co-authorship analysis of authors on Scopus bibliographic data. To avoid duplication of names (e.g., daly h. and daly he.), I created a thesaurus file following the example of the thesaurus_authors.txt file in the data folder, and then loaded it when the software asks me to.
    I created the thesaurus file on excel, saving it as a tab delimited file.
    Nonetheless, after running the analysis, results are the same to the analysis without the thesaurus file.
    Could you please give me some advice on how to make this work?
    Thank you very much for your help.
    • Ludo Waltman October 20th, 2018 8:42 pm
      Could you please send your files to I will then take a look at your problem.
      • Flavio October 20th, 2018 8:55 pm
        I just sent the e-mail.
        Thank you very much!
  • PJH October 17th, 2018 1:17 am
    I am trying to understand the difference between the 'population of documents' on which citation and co-citation analysis are based.
    As I understand it, traditional citation analysis limits the population of citations to the database in which the citation analysis being conducted. Thus, we talk of Scopus citations or WoS citations etc.
    In contrast, co-citation analysis of documents is based of a 'broader reach' of documents. Thus, co-citation analysis conducted on a sample of studies drawn from SCOPUS will often yield documents that are not included in SCOPUS.
    MY QUESTION is what is the population of documents beyond Scopus (or Wos) that VOSviewer examines in order to generate co-citations?
    Co-citation analysis is new in my field and the journal reviewers are rightfully asking for detailed elaboration of the methodology.
    • Ludo Waltman October 17th, 2018 7:21 am
      You are right. Co-citation analysis considers a broader universe of documents than (direct) citation analysis and bibliographic coupling analysis. Co-citation analysis takes into account the references of documents indexed in databases such as Web of Science and Scopus. Hence, unlike citation analysis and bibliographic coupling analysis, co-citation analysis takes into account documents that are not themselves indexed in one's database but that are cited by documents that are indexed in the database.
  • Antoine October 15th, 2018 10:52 am
    Amazing software! Thanks for the hard work!
    Is it possible to extract and export the publications belonging to each item and cluster?
    • Ludo Waltman October 15th, 2018 3:16 pm
      What kind of map do you have? For instance, do you have a term map, a co-authorship map, or a citation-based map, and what is the unit of analysis in your map (e.g., authors, journals, etc.)?
  • Anton October 4th, 2018 8:02 am
    Dear developers,
    Thank you for your wonderful software, it makes life much easier for researchers! I have a small query in regards to making the maps available online, section 5.2. I have followed the exact steps, however, when downloading and opening the files, i get an error: "Error while reading VOSviewer map file (line 1): Column header is empty". I used Google Drive, Box, free online file sharing websites, with the same error. This is a map example that i have:
    This is one of the ways i tried to make it available online (without the network map, which i also tried with the same error) to no avail.
    Please let me know what i have done wrong.
    Kind regards,
    • Ludo Waltman October 4th, 2018 11:46 am
      I have tried out the URL. I am unable to access the map file. It turns out that a log in is required. This is why VOSviewer is unable to read the map file and why you get an error.
      • Anton December 4th, 2018 6:20 am
        Hi Ludo,
        I have tried different options to no avail. For example, I have made the map available to public via Google Drive as well as direct download. Neither require passwords. When clicking the link the software says "Error ...: File cannot be found". However, the link (for the map) itself seems to work and download fine: (direct download link) or Any comments are greatly appreciated.
        Kind regards,
  • Peter LR September 28th, 2018 9:42 am
    Hi! Congratulations for your work.
    I wonder if it is possible to export a list of the items by cluster.
    Thank you so much!
    • Peter LR September 28th, 2018 10:48 am
      I've just realized I can find the information in map files.
      Thank you!
  • John Paul SanGio September 20th, 2018 4:55 pm
    Thank you for offering this excellent resource.
    I am constructing a co-authorship map.
    I would like to display all authors with whom I have ever published.
    My current map (generated by default settings) contains only those authors with whom I have published a number of times.
    I would appreciate guidance on how to display all co-authors.
    John Paul
    • John Paul SanGio September 20th, 2018 8:34 pm
      VOSviewer Staff:
      I solved the problem (found the options with the Web of Science input format).
      There is no need to respond.
      John Paul
  • Ana September 11th, 2018 12:42 am
    Good night,
    Could you please explain me the meaning of "total link strength"?
    I am using VosViewer to do a co-citation analysis (cited references) and a column named "total link strength" appears (next to citation) ???
    Thank you very much!
    Best regards.
    • Ludo Waltman September 11th, 2018 7:30 am
      This is explained in Chapter 2 of the VOSviewer manual. If this explanation is insufficient, then please let me know.
      • Ana September 11th, 2018 10:40 am
        Hello Ludo,
        Thank you for your answer!
        I already had the Vosviewer manual, but I was asking because in the manual it refers to:
        bibliographic coupling links
        co-authorship links, and
        co-occurrence links

        But it is not clear to me in the case of co-citations (refrerences), whats the meaning of "total link strenght"

        Hoping you me can help me.

        Thanks a lot!
        • Ana September 11th, 2018 6:49 pm
          Thanks for everything. I found the information!
      • Maurício November 11th, 2018 3:55 pm
        But how the total link strength is calculated? I research in the manual but I didn't found this information!
        Best regards
        • Ludo Waltman November 11th, 2018 7:20 pm
          A brief explanation is provided on p. 5 in the VOSviewer manual:
          "There are two standard weight attributes, referred to as the Links attribute and the Total link strength attribute. For a given item, the Links and Total link strength attributes indicate, respectively, the number of links of an item with other items and the total strength of the links of an item with other items. For example, in the case of co-authorship links between researchers, the Links attribute indicates the number of co-authorship links of a given researcher with other researchers. The Total link strength attribute indicates the total strength of the co-authorship links of a given researcher with other researchers."
          In other words, in the case of co-authorship links, the Links attribute of a given researcher equals the number of researchers with whom the focal researcher has co-authored one or more publications. The Total link strength attribute of a given researcher equals the sum over all other researchers of the number of publications co-authored with the focal researcher. Definitions for other types of links (citation, bibliographic coupling, co-citation, co-occurrence) are analogous.
          • Mauricio November 18th, 2018 9:38 pm
            Thanks Ludo
            Now I understand. In the manual it wasn't so clear.
            Best Regards!!
  • Breno Prata September 9th, 2018 4:31 am
    Good night,
    I am trying to create a web integration between VOSViewer and Gephi, I want it all to work as simple as possible, I want to import a csv file from scopus into VOSViewer and generate a map, after that export that map to a supported Gephi format. But I can't quite find that code on the JAR source file, is that any way to help me find those specific code, it would really make a diference if I managed to unite these two tools :)
    • Ludo Waltman September 9th, 2018 9:03 am
      The source code of VOSviewer currently is not available. The software is not open source. We plan to release the source code within the coming months.
  • Hai Giang Ha September 7th, 2018 9:44 am
    Dear Mr. Ludo Waltman,
    Could you please tell me how I can explain the relationship of items in a cluster? How was the color of a cluster assigned? And Is there anyway if I want to change the position of one item?
    I need that information to explain in my report.
    Thank you so much and I am looking forward to hearing from you.
    Best regards,
    Hai Giang Ha
    • Ludo Waltman September 7th, 2018 7:25 pm
      Your question is a bit general. Some answers are provided in the VOSviewer manual and in the book chapter available above. If these answers are insufficient, then please let me know.
  • Philip Hallinger August 28th, 2018 5:32 pm
    Great program.
    I have not had any issues up to now. However when I upload a scopus file, I keep getting an error message that there is an incorrect number of rows in record 367. I went and deleted record 367 in scopus. Now it says the error is in record 368.
    What's the problem and the solution, please.
    • Ludo Waltman August 29th, 2018 7:43 am
      Could you please send me your file ( I will then take a look at it and offer advice on this issue.
      • Philip August 29th, 2018 8:19 am
        Thanks for the prompt response. Although I am an absolute newbie at this I found a workaround for the problem.
        The database was only 700+ documents, so I exported 200 at a time to 4 files and uploaded the four files. it worked. So although I don't know what the 'problem' actually was, I don't have it anymore and I'm a happy guy.
        So thanks again.
  • Alberto August 23rd, 2018 10:22 am
    Hi! Thank you for your work on VOSviewer.
    I'm wondering if it is possible to create a co-citation keyword map based on a personal library of papers.... I mean, not taken from scopus or wos, but, for example, from a .bib file. Keywords are there, so I'm wondering if a way to do that actually exists.
    • Alberto August 23rd, 2018 10:39 am
      I did it with .RIS file very easily from Endnote! Thanks!
  • Robyn August 22nd, 2018 6:43 pm
    Hello, I'm working on cleaning up a small set of citations using a thesaurus file. I've reviewed the sample thesaurus files provided, and taken the suggestions in the comments made previously of creating a tab delimited file using Excel. However, when I create my visualization, instead of replacing the terms outlined in the thesaurus file, it simply removes them from the visualization altogether.
    It was my understanding that the "replace by" column would allow me to collect together the alternate spellings/ plurals into on term - not remove the terms entirely. Have I misinterpreted the purpose? Is there a strategy you would suggest to resolve this issue?
    Many thanks!
    • Ludo Waltman August 22nd, 2018 9:59 pm
      Your interpretation is fully correct. Could you please send your thesaurus file to I will then take a look at the file and try to offer some advice.
    • Alberto September 9th, 2018 9:50 pm
      Hi Robyn,
      could you please tell me where I can find the thesaurus samples?
    • Diana October 18th, 2018 4:46 pm
      Hello, Robyn. Would you succeed with your thesaurus? I am working with the same task. Could you share your Excel file to look how it is created?
      Thank you.
  • Giuseppe Vito August 19th, 2018 5:37 pm
    Dear Ludo,
    Thanks for the reply.
    The txt files I intend to make available on-line are those generated by Vosviewer in the analysis of bibliographic coupling, cocitation, etc. (... map.txt and ... net.txt) of publications of the department I belong (exactly as discussed in section 5.2 of the manual). Currently the aim is to divulge bibliometric maps to colleagues of the department, subsequently I intend to integrate some of my publications with links to the related Vosviewer maps.
    In the meantime I solved the problems with github, which constantly flagged my account by mistake: I'm sorry for the request made to you.
    On this occasion:
    using excel to read a file ... map.txt (eg. bibliocouplingmap.txt), the format of the individual cells of the columns weight and score is not unique and I cannot transform them into one numerical format as I would like to perform further reflections.
    is it possible to generate a network file in full format (pages 38-39 of the manual version 1.6.8) instead of sparse format?
    Thank you very much for the attention you will dedicate to me.
    • Ludo Waltman August 19th, 2018 5:47 pm
      Your Excel problem probably relates to the regional settings of your operating system. The easiest way to solve the problem then is to change the regional settings. You need to make sure that a period, not a comma, is used as the decimal separator.
      Saving a network file in the full format is not supported by VOSviewer. VOSviewer can open network files in two formats, both the sparse and the full format, but it always saves these files in the sparse format.
      • Giuseppe Vito August 19th, 2018 5:55 pm
        Thanks for the immediate reply, I will try to change the settings in Excel and I will let you know
  • Giuseppe Vito August 16th, 2018 5:43 pm
    Dear Ludo and Nees Jan, first of all my congratulations for your work and my best wishes for future developments. I encounter problems in making txt files available online. I have used github but I am not fully satisfied with this software. Could you kindly suggest alternative ways of doing this? Best Regards. Giuseppe Vito, Parthenope University, Naples, Italy
    • Ludo Waltman August 19th, 2018 1:23 pm
      I think I need a bit more information to answer your question: What kind of text files do you want to make available online, and for what purpose? Do you mean that you are trying to make a map available online, as discussed in Section 5.2 of the VOSviewer manual? And why exactly are you 'not fully satisfied' with GitHub?
      • Giuseppe Vito August 19th, 2018 5:33 pm
        Dear Ludo,
        Thanks for the reply.
        The txt files I intend to make available on-line are those generated by Vosviewer in the analysis of bibliographic coupling, cocitation, etc. (... map.txt and ... net.txt) of publications of the department I belong (exactly as discussed in section 5.2 of the manual). Currently the aim is to divulge bibliometric maps to colleagues of the department, subsequently I intend to integrate some of my publications with links to the related Vosviewer maps.
        In the meantime I solved the problems with github, which constantly flagged my account by mistake: I'm sorry for the request made to you.
        On this occasion:
        1) using excel to read a file ... map.txt (eg. bibliocouplingmap.txt), the format of the individual cells of the columns "weight " and "score " is not unique and I cannot transform them into one numerical format as I would like to perform further reflections.
        2) is it possible to generate a network file in full format (pages 38-39 of the manual version 1.6.8) instead of sparse format?
        Thank you very much for the attention you will dedicate to me.
  • Fernanda August 13th, 2018 5:18 am
    I am trying to download the VOSviewer for windows at this site. Althoug, my computer detected a virus
    The name is Trojan:Win32/Vigorf.A
    Is it safe to make the download here?
    Is there any problem with the website?
    • Ludo Waltman August 13th, 2018 1:24 pm
      A number of VOSviewer users have reported this problem. We have investigated the problem in detail. The software is safe, and the threat warning given by Windows Defender is incorrect. We have added a brief explanation on the Home page and also on the Download page.
      • Ludo Waltman August 19th, 2018 1:24 pm
        We have been in contact with Microsoft's Windows Defender team and the problem has now been solved.
  • Ranbir August 10th, 2018 11:58 am
    Dear Friends
    If anybody can help me to answer
    Out of ---first author co-citation data and all-author co-citation data, which one is used by VOSviewer ?
    Your advice can very helpful for me
    • Ludo Waltman August 10th, 2018 12:11 pm
      In the case of Web of Science data, only the first author is considered (since information on other authors is not available in Web of Science data). In the case of Scopus data, all authors are considered.
      • Ranbir August 10th, 2018 12:39 pm
        Thanks a lot Dear Ludo Waltman
        Thanks again
  • Anthony Molisani July 26th, 2018 5:45 pm
    Hi Dr Waltman,
    I really appreciate the text mining features of VOSviewer, In doing the analysis, I would like to further explore the publication metrics associated with the clusters of words. To do this, I need to know which publications are associated with each term. I'm having trouble finding such a way to identify/export theses relationships between publications-mapped terms. Any advice would be incredibly helpful!
    • Ludo Waltman July 26th, 2018 6:16 pm
      In the last step of the 'Create Map' wizard, a table is presented that shows the terms that will be included in your term map. It is possible to right-click on this table. A context menu will then appear that offers the possibility to save the links between terms and documents. This seems to be exactly what you are looking for. Let me know if you need further information.
      • Anthony Molisani July 26th, 2018 7:50 pm
        Hi Dr Waltman,
        That is perfect. Thank you!
        Regarding document id numbers, I imagine they are assigned based on the row within the upload document. How are they assigned when using multiple files when uploading records into VOSviewer?
        Thanks, again. This is extremely helpful!
        • Ludo Waltman July 26th, 2018 8:00 pm
          When you have multiple input files, the document IDs are dependent on the order in which your files are processed by VOSviewer, and this order is not visible to the user. In this case, it is therefore best to manually merge your files into a single input file. The document IDs then correspond in an unambiguous way to rows within your input file. Note that, if your input file includes a header line (as is the case for Web of Science and Scopus files), the first document is located on the second line in your file and the ID of this document is 1. The document on the third line has ID 2, and so on.
          • Anthony Molisani July 26th, 2018 9:06 pm
            Excellent. Thank you very much!
  • Hai Giang Ha July 15th, 2018 12:17 pm
    Dear Mr. Waltman,
    I am now using this wonderful tool for bibliometric analysis. The records download from the Web of Science are quite large, about 250,000 records. When I insert the records, the system informed that I need to extend the memory. I have read the manual, yet, I could not find VOSviewer JAR file as well as the command line.
    Could you please tell me where I can download the VOSviewer JAR file and the command line?
    I am looking forward to hearing from you.
    Thank you so much.
    Hai-Giang Ha
    • Ludo Waltman July 15th, 2018 1:39 pm
      The JAR file can be downloaded from the VOSviewer website. It is referred to as the VOSviewer version for other systems (i.e., not for Windows or for Mac systems). In principle, the Windows and Mac versions of VOSviewer should already make use of most of the internal memory available on your system, so I am not sure whether the use of the JAR file will solve your problem. I am wondering what kind of map you would like to create based on your 250,000 records. If you could provide me with some more details, I may be able to offer some further advice. It would also be helpful for me to know you much internal memory you have available on your system. (By the way, the amount of internal memory that is made available to VOSviewer can be found in the bottom part of the 'About' dialog box in VOSviewer.)
      • Hai Giang Ha July 15th, 2018 5:24 pm
        Thank you so much for your quick reply.
        The amount of internal memory that I found in the 'About" dialog box is 'Memory usage: 37/ 746 MB'.
        I want to create an (author) keywords co-occurrence and countries co-authorship network.
        • Ludo Waltman July 15th, 2018 7:17 pm
          746 MB is a small amount of memory. This may cause problems even for data sets much smaller than yours. How much internal memory does your computer have in total? Do you have many other programs that are running simultaneously with VOSviewer?
          • Hai Giang Ha July 16th, 2018 5:17 am
            I have installed VOSviewer on my other computer, driver D. Its volume is 537 GB, and it has 515 GB free. The system information: RAM 8GB. Memory usage this time somehow is better '44/ 989 MB'. However, I still can not create the maps with that 250,000 records. When I used VOSviewer, I closed almost programs but MS Word, MS Excel, and Chrome.
            Thank you
            • Ludo Waltman July 16th, 2018 9:34 am
              Thanks for the additional information. Based on this information, it seems that you are probably working with a 32-bit version of Java. In order to get access to more internal memory, you need to use a 64-bit version of Java. This means that you need to update Java on your system,. My recommendation is to update to the most recent 64-bit version of Java 8. (Do not use Java 9 or 10.)
              • Hai Giang Ha July 19th, 2018 10:57 am
                Thank you so much for your suggestion.
                After reinstalling Java 8 64-bit for Window, it really worked. When I checked "About", it stated "Memory usage: 109/4132MB". I uploaded the 250,000 records, it loaded 99% and then stopped (before it was only 32%).
                Do you have any solution for me?
                • Ludo Waltman July 19th, 2018 11:49 am
                  I am glad to hear that 64-bit Java works better. It seems that you still don't have enough memory to process such a large data set. I think you need to either reduce the size of your data set or find a computer with more internal memory. I hope this is possible for you.
                  • Hai Giang Ha July 22nd, 2018 8:08 pm
                    Thank you for spending your precious time to help me.
                    I install VOSviewer on other computer and it worked.
                    I do appreciate what you and your team have done for the global scientific research.
  • Fatima Noora July 6th, 2018 8:55 pm
    Dear Mr Waltman,
    Could you kindly advise on the way to create Thesaurus file? (the simplest possible, please)
    I am stuck because of the many synonyms, spelling differences and abbreviated terms I've in my Scopus data base.
    Thanks in advance,
    • Ludo Waltman July 6th, 2018 11:07 pm
      When you download VOSviewer, you will obtain a ZIP file that includes two examples of thesaurus files. Please take a look at these examples. Let me know if you have any questions based on these examples.
      • Fatima Noora July 6th, 2018 11:12 pm
        I already did! they are terms and authors.
        My question is how to create a file like this?
        • Ludo Waltman July 6th, 2018 11:22 pm
          It is easiest to create such a file using a spreadsheet program, for instance MS Excel. Make sure to save your thesaurus as a tab-delimited text file.
          • Fatima Noora July 6th, 2018 11:48 pm
            Well noted!
            Thank you so much.
  • William Sanger July 5th, 2018 7:23 pm
    Hi M. Waltman,
    First of all, thanks for such amazing tool VOSviewer is. I've been using it for the past 2 years to visualize batchs of academic papers, which was great.
    I have a question. I cannot do usual visualizations with VOSviewer using Web of Science exportation tool (5K). Now, when I export papers, it only shows the title, the author and the source. I do not have access to the keywords anymore. The same goes with "save to other file formats".
    Do you have any insight about such situation? If so, do you know any alternative?
    Best regards, and thanks a lot again,
    • Ludo Waltman July 5th, 2018 7:35 pm
      Using the 5K option, files exported from Web of Science do not provide full publication records. To obtain full publication records, you need to use the ordinary export feature of Web of Science, where downloads need to be done in batches of at most 500 records. I am afraid this is the only solution. When you use the ordinary export feature of Web of Science, it is possible to download full publication records. VOsviewer will then be able to create keyword co-occurrence maps and other types of maps that cannot be created based on incomplete publication records.
      • William Sanger July 9th, 2018 2:53 pm
        Thanks a lot,
        Have a great day,
  • Shivam June 28th, 2018 8:59 pm
    Dear Sir,
    can a VOS viewer be done for the Data downloaded from google scholar using publish and perish tool in csv format ?
    or what other methods can be used to do an analysis for google scholar data ?
    • Ludo Waltman June 28th, 2018 10:06 pm
      Yes, it is possible to work with Google Scholar data in VOSviewer. This can be done by downloading data from Google Scholar using Publish or Perish and by saving the data in a RIS file. Unfortunately, the possibilities for analyzing Google Scholar data in VOSviewer are limited. In particular, it is not possible to create citation-based maps based on Google Scholar data.
  • Ilenia June 26th, 2018 7:25 pm
    I would like to use VosViewer for my research, however I am having issues in uploading files from Scopus.
    I did my research on scopus and I exported in a CSV file all information that Scopus allows me to export i.e. citation, bibliographic information, etc. When I open the downloaded file I can see all the details of the papers I selected in my search. When I upload the file in VosViewer and I try to create a term map VosViewer displays this message: "Error while reading Scopus file: file is empty". I do not understand what is the problem since I have not changed anything in the downloaded file. Could you please help me with this issue?
    I thank you in advance.
    Best regards,
    • Ludo Waltman June 26th, 2018 10:20 pm
      Could you please send your file to I will then take a look at your problem.
      • Ilenia June 27th, 2018 1:10 am
        Hi Ludo,
        I thank you for your reply but it seems that I sorted out the problem. I had to make sure that the content in the first cell of the first row was split in different colomns. Once that I did this, the software is now working.
        Best regards,
  • Jasmijn June 25th, 2018 1:55 pm
    Hi there,
    Could you give me some advice on the following?
    I learned about VOSviewer through a colleague and wonder whether the software is suitable for a literature review I'm currently conducting:
    After a systematic search I've ended up with a small dataset of 45 suitable references. I notice an immense range of operationalizations for the same concept that are used by these references and want to delve further into this issue. I want to visualize the different measurements, group them and show how many references use the same measurement. I think there are several islands of measurements that are used by the same authors and I would like to map this. I then would like to see whether the references cite each other and how many references build bridges to other islands of measurements.
    Would it be possible to create the network maps I'm looking for in VOSviewer or does the software only produce maps based on references as data? I guess that my research interests would require me to create and import data (measurements) that I would have to construct myself. Based on what I read on VOSviewer so far, I am not certain whether the software is suitable for this specific literature review.
    Thank you very much for considering my request.
    Best wishes, Jasmijn
    • Ludo Waltman June 25th, 2018 6:38 pm
      Although I don't fully understand what kind of visualization you would like to create, I do think it is possible to create such a visualization using VOSviewer. However, this will require an in-depth knowledge of VOSviewer, since you will need to do considerable preprocessing of your data to provide the data to VOSviewer in the right way. If you do not yet have a substantial experience in working with VOSviewer, then I think creating the visualization you have in mind will be quite challenging.
      • Jasmijn June 26th, 2018 10:23 am
        Thank you very much for your swift reply! This is helpful in deciding what to do. Best wishes, Jasmijn
  • Lara June 23rd, 2018 12:32 am
    Hi there,
    I've been using VOSViewer for a couple of years now, and I really like what you can do with it. However, I find myself unable to use it for graphic analyses of co-citations (i.e., nb of times specific papers get cited in a series of references). I've tried to upload databases with .RIS and .CSV extensions but I can't seem to get it right: I never get the option to analyse co-citations (only co-authorship and co-occurences). What is the right format to run a bibliomeric analysis of co-citations? If the source should be .CSV, what should my table look like?
    Thanks for your advice,
    • Ludo Waltman June 23rd, 2018 12:42 am
      Citation-based analyses indeed are not supported for RIS files. This is because RIS files do not contain reference data in a standardized format. Citation-based analyses are supported only for Web of Science files, Scopus CSV files, and Crossref JSON files.
      • Lara June 23rd, 2018 12:51 am
        Thanks a lot for your prompt response! Ok, it makes sense. However, none of these research databases (WoS, Scopus and Crossref) provides the exact list of refs. Is it possible to build the file manually? Is there a sample I can follow?
        • Ludo Waltman June 23rd, 2018 7:43 am
          I am not entirely sure what you mean by "none of these research databases (WoS, Scopus and Crossref) provides the exact list of refs". What do you mean by "the exact list of refs"? Anyway, in order to have an example, just download a file from Web of Science or Scopus and use that file as an example. Please keep in mind that you need to follow exactly the file format used by Web of Science or Scopus, including the format used for specifying references. Otherwise VOSviewer will not be able to process your data.
          • Lara June 23rd, 2018 4:13 pm
            Ok, noted. Thank you for your help!
  • Allison June 22nd, 2018 6:57 pm

    How I can download a CSV file of a map I have created in VOS viewer? I would like to download the data used to create the map and use this to calculate some statistics.
    Thank you!
    • Ludo Waltman June 22nd, 2018 8:15 pm
      Use the 'Save' button on the 'File' tab to save your map in a map and network file. These are plain text files with tab-delimited columns. Please see the VOSviewer manual for more details on the map and network file formats.
  • rinrin June 17th, 2018 2:26 am
    The VOSviewer manual refers to txt files (says "see....txt file) throughout. Where are these txt file example located so that I can view them?
    • Ludo Waltman June 17th, 2018 9:02 am
      When you download VOSviewer from the website, you will obtain a ZIP file that includes these text files.
  • Andy Yeung May 31st, 2018 1:12 am
    Hello everyone,
    I conducted a bibliometric study using VOSviewer. Journal reviewer's main concern is the use of a single database, Scopus. S/he mentions that I should search multiple database to avoid missing some highly-cited papers not indexed in Scopus. Suppose I also search WoS, then a lot of papers will have two distinct citation counts... how should I merge them altogether for the overall analysis, e.g. top-100 list, country and journal performances?
    Many thanks and best wishes,
    • Ludo Waltman May 31st, 2018 8:03 am
      Merging two different data sources is highly challenging. You need to have an extensive expertise on the data formats used by the different data sources in order to be able to merge them. My recommendation is not to take this approach. It probably will be too difficult and too complex. Although I don't know the details of your project, I think it is best to use only the Scopus database. In almost all cases, publications that are in Web of Science are also in Scopus, especially highly cited publications, so I do not expect that adding Web of Science data has a substantial effect on your study.
      • Stephan De Spiegeleire June 3rd, 2018 2:39 am
        Hmm. Disappointing answer. I think the issue raised here is a quite important one - we're running into similar issues in a large project. One of the ways in which we hope to solve this problem is via Zotero and the update to the DOI plugin that Brenton Wiernik is planning to make that will allow the user to automatically add DOIs to Zotero items through the CrossRef OpenURL API. If VOSviewer could include something similar, that would really be great. 
        Another option - used by VantagePoint and CiteSpace, for instance - might be to use fuzzy logic, with a degree of conservatism that the user can define, to generate an initial list of potentially matching authors (or organizations, etc. -whatever fields have to be 'cleaned'). The user then review the list and either approve or have the ability to move one or more of the entries that are 'preliminarily matched' to where they should be. 
        Finally, we are also looking into more generic tools like OpenRefine (formerly Google Refine), which might also do the trick.
        But so I certainly hope VOSviewer will look a bit deeper into this, as it is otherwise a really powerful and relatively intuitive tool! 
        • Ludo Waltman June 3rd, 2018 10:03 am
          I think it would not be fair to give the impression to VOSviewer users that the problem of merging data from Web of Science and Scopus can be solved in an easy way. We need to acknowledge that there is no easy solution. The problem of course can be solved, but this requires considerable technical skills. Most VOSviewer users do not have these skills.
          Also, merging data from Web of Science and Scopus is of limited interest, since to a large extent Web of Science is a subset of Scopus, at least under the assumption that Web of Science is to be understood as Web of Science Core Collection and that the analysis focuses on publications going back at most 20 years.
          Because of the above two reasons, from a practical point of view, my recommendation to the typical VOSviewer user is to work with a single data source.
  • Ghaliamus May 29th, 2018 1:37 am
    Many thanks for your appreciated work behind such amazing bibliometrics tools.
    Let me please ask about two possible explanations by which I can understand my resulted network analysis. To make my question clear, if you don't mind, I will use the produced network figure, you put on your VOSviewer tutorial cover, as example. Let us assume the network is based on WOS data. Let us assume the network is a network of sources (journals, conferences, etc ..) and the links between such sources (nodes) are based on the citations go and back between every two nodes. The two needed interpretations, if you can provide please, are:
    (1) The clusters: what is the explanation of having two sources such as Nature and Science in one cluster? or having PLoS ONE in a different cluster? I read your tutorial and read about the clustering techniques. However, my question could be considered a question from layman who wants only to understand what WOS data were important in putting two sources in one cluster or in different clusters? Was the data the keywords? the title? only the number of citations?
    (2) The distances between any two nodes, regardless they are in same cluster (colour) or in different cluster: what is the explanation of having two nodes near each other or far from each other? what makes Journal of Geoghysical Research near Sensors journal but not near The Plant Journal? Again, was the reason the citations number or the documents content (such as abstracts) or the authors?
    I'm sorry if I'm asking about the obvious. With your appreciated kindness, I wish you can give me such explanation. Many thanks and my best wishes.
    • Ludo Waltman May 29th, 2018 6:33 am
      Both the clustering (i.e., the coloring of the items) and the layout (i.e., the positioning of the items in the two-dimensional space) are based exclusively on the underlying network data, so the citation links between journals in your example. Hence, journals that are in the same cluster tend to be strongly connected to each other by citation links. Likewise, journals that appear close to each other in the layout tend to be strongly connected to each other by citation links.
      • Ghaliamus June 5th, 2018 3:36 pm
        Hello Mr Ludo, many thanks for your appreciated response and its explanation. I beg your patience with me trying to learn. Before I write this reply I went back to your references focusing more on understanding the VOS algorithm and comparing it to other techniques. Generally, what I got was that the optimization with VOS is to maximize the distance in the map between distinct items and minimize the distance in the map between similar items. Until this point, I can understand what is the meaning of having two journals near each other in a produced map. However, I couldn't figure from my reading the clustering interpretation. And what I got from your kind response that if two items are in one cluster they are relevant and if two items near each other in the map regardless of their clusters they are also relevant. Good. What I want to distinguish is in the following case:
        A map with several items (T) and clusters (C). Focusing on T1, T2 and T3 where T1 and T2 belong to Ca and T3 belong to Cb. According to the distance, however, T2 is near T3 while T2 is far from T1.
        My question is:
        Which one of the following statement is true:
        Statement 1: T2 is relevant to T1 more than T3.
        Statement 2: T2 is relevant to T3 more than T1.
        Statement 3: cannot quantify the difference relevancy of T2 with T3 and T2. Enough to say it is relevant to T2 and T3 without any differentiation.
        • Ludo Waltman June 7th, 2018 9:46 am
          Good question! I would choose statement 3. In your example, the layout and the clustering provide contradictory information. In itself, this is understandable. The layout and the clustering both provide a high-level summary of a complex data set. In summarizing the data, some information is getting lost, and this is why the layout and the clustering do not always provide consistent results. When this happens, the implication is that it is not possible, based only on the layout and the clustering, to draw a clear conclusion on the relatedness of the different items.
          • Ghaliamus June 10th, 2018 10:27 pm
            Hello Mr Ludo, many thanks for your patience and explanation, your time is appreciated. If I got your point, it seems that the situation I presented above requires the input of a domain expert while the layout and clustering were not enough. Thank you again for the answer. Good luck.
  • Sushma Dhital May 2nd, 2018 4:28 am
    Hello, I am having a trouble. I used web of science data to analyze the citation by documents in Vosviewer. But the xcel has citations written as 'total citations' number greater than what I see in Vosviewer. Why is there the difference? What citation by documents refers to in vosviewer. for instance, i found the result 4081 total citation in xcel and 3891 in vosviewer.
    • Ludo Waltman May 2nd, 2018 5:29 pm
      Could you please explain your question in more detail? A detailed step-by-step explanation of the analysis that you are carrying out would be helpful. At the moment, I am afraid I don't fully understand your question.
  • Shivam Mani Tripathi April 29th, 2018 5:19 pm
    Dear Sir/ Madam,
    As part of a research article,i am doing a syntometric analysis of google svholar data for the author BS Kademani.
    i have downloaded the details of all his papers including his titles,Coauthors,citations,Source Journals and year of publication.
    i Wanted to do a VOS viewer for this set of data,but as this format is not being supported by the software,how do i proceed further ?
    i wanted to find out the coauthorship network and words network fro this data set.
    Kindly help.
    Shivam Mani Tripathi
    Student Msc
    South Asian University
    New Delhi.
    • Ludo Waltman April 29th, 2018 7:01 pm
      My recommendation is to use the Publish or Perish tool to download data from Google Scholar and to save this data in a RIS file. The RIS file can then be processed by VOSviewer.
  • d April 28th, 2018 11:35 pm
    Is it possible to use Vosviewer to analyze data collected from JSTOR?
    • Ludo Waltman April 29th, 2018 12:04 am
      VOSviewer doesn't provide support for JSTOR data. You need to take care yourself of converting the data to a file format that is supported by VOSviewer.
  • Angela April 25th, 2018 12:05 pm
    I am new at VOSviewer and I am doing a bibliometrics analysis about a specific theme on psychology. I have done search in three data bases (WOS, ERIC and MedLine) but I do not know if it is possible import the data of these three data bases and how could I do it. For example: Can I create a excel file with all columns of WOS File and add rows with the information of the others articles that I found in others data bases?
    • Ludo Waltman April 26th, 2018 10:17 am
      As you probably know, VOSviewer offers direct support for Web of Science data and for PubMed data (using the Medline file format). ERIC data perhaps can be saved in the RIS file format. RIS files are supported by VOSviewer. Combining different data sources is always challenging. It requires an in-depth understand both of the various file formats and of VOSviewer. If you are interested in producing term co-occurrence maps, different data sources can be combined by creating a VOSviewer corpus file. If you are interested in producing other types of maps, then unfortunately there is no easy way to combine different data sources. Converting data to the Web of Science file format in principle is possible, but in practice this is rather challenging. I do not recommend this approach, unless you are very experienced in advanced data processing.
  • Maria P. April 17th, 2018 12:01 pm
    I am interested in making a co-authorship map with data downloaded from SCOPUS. I have seen this option is not supported for the current vosviewer version. Is there a way of downloading the 1.6.5 version? The reason I want to use SCOPUS data is that I can easily download all articles from the institution where I work from SCOPUS (we have an scopus institution ID, and all our articles are associated) but not with Web of Sciences (researchers write the affiliation address in too many different ways). thanks!
    • Nees Jan van Eck April 19th, 2018 10:32 pm
      VOSviewer version 1.6.5 can be downloaded using the following links:
      Other systems:
  • Amin April 6th, 2018 1:27 pm
    Dear Ludo,
    I am having difficulty with the export from web of knowledge to VOSViewer. When I choose "export to other formats" --> "records (1-269)"--> "Full record and cited references" --> "tab-delimited (win)" --> "Send"
    Then in the software I try to "create a map based on the bibliographic data" --> --> in the web of science tab I choose the text file---> citation -document
    Then instead of the number of 269 records I end up with 219.
    I tried to extract info to Endnote and indeed the number of records are 219!
    I am puzzled of why from 269 records in Web of knowledge only 219 show up in the export process.
    If I export " "Full record" then it comes with 269 records.
    However, then I cannot make a citation document map. Do you have any suggestion?
    • Mihaela April 6th, 2018 10:52 pm
      Hello Amin,
      I recently tried to work with web of science and I am having similar problems with "Full record and cited references". It either exports a empty tab-delimited, one were first column headers are "null", completely missing headers, or in the happy event were everything is ok some records missing. I think its a wos problem at export. I managed to work around by exporting batches of 6-14 articles at a time, but its hard work and i only have around 200 articles. I cant imagine doing the same with a large sample of articles.
      To note that a few months ago everything worked ok.
      • Amin April 7th, 2018 7:16 am
        It also worked for me few months ago. I tried to extract them in smaller batches of 50. I would do it with what you suggested. Many thanks.
        • Ludo Waltman April 7th, 2018 7:22 am
          I'll do some further investigation of this problem. As a temporary workaround, my suggestion is to export data from Web of Science in plain text format instead of tab-delimited format. VOSviewer also supports the plain text format.
          • Amin April 7th, 2018 9:43 am
            Dear Ludo
            I I tied and an error returned
            Error while reading web of science file File is invalid
            • Ludo Waltman April 7th, 2018 10:28 am
              Amin, Mihaela, could you please send some examples of invalid files to This will help me to investigate the problem. Thanks!
              • Amin April 9th, 2018 11:33 am
                Dear Mihaela and Ludo,
                I tried to export records in smaller batches of 10. However, it seems the problem still persists. I figured out that some of the records have a value of (null). So, I miss some of the information on the citation data for some of the results. The only thing that I can do is to skip that particular record. Michaela: Can you confirm that this also the case for you?
                • Ludo Waltman April 9th, 2018 12:02 pm
                  Brief update: It is clear now that the problems occur both in tab-delimited files and in plain text files. Indeed, as indicated by Amin, one of the problems is the appearance of 'null' strings in the files. Another problem relates to records that are missing in the files. I am in contact with the Web of Science team and they are investigating these problems.
                  • Amin April 9th, 2018 12:33 pm
                    Dear Ludo,
                    In my search I found out that only two records are missing (as null). However if I want to export at once then from 269 only 219 records would be there. Somehow it seems that Web of Knowledge export function does the job in batches. So, if in one of the batches there is a NULL record then the whole batch comes at NULL. In my search records 74 and 210 are NULL. I cab send you the search phrase if needed.
                    • Mihaela April 11th, 2018 2:11 am
                      Sorry for not giving feedback, i was out of town for hollyday. I will send some examples to you Ludo. Amin i suspect the same, batches download. I started with larger batches and then downscaled. In some parts i had to take the articles one by one, and in the end i am only missing around 10 articles out of 250. But i had the whole list of titles downloades before so i searched after the title.
                      • Ludo Waltman April 19th, 2018 7:58 pm
                        Clarivate Analytics has informed me that the problem with the Web of Science export has been fixed. If you still experience difficulties, please let me know.
                        • Mihaela April 19th, 2018 8:01 pm
                          Thank you Ludo,
                          I will try as soon as possible.
  • Patrick Zawadzki March 31st, 2018 5:50 pm
    Hello Ludo! Congrats for this great software, you are doing a great job.
    We just started to use it and found problems on how to do some interpretation.
    When using co-ocurrence of authors keywords some networks shows keywords from different clusters, if the cluster is a correlation between keywords why this happens?
    • Ludo Waltman March 31st, 2018 10:03 pm
      I am afraid I don't understand your question. What do you mean by "some networks shows keywords from different clusters"?
      • Patrick Zawadzki April 17th, 2018 1:43 am
        For example, we found a network with three nodes, first and second nodes are inside red cluster, and, the third node is inside blue cluster. Our analysis is looking for associated keywords in a specific new area, it is better to use the cluster ou the network results as parameter to decide better association?
        PD: sorry about my poor english.
        • Ludo Waltman April 17th, 2018 2:46 pm
          The network structure offers the most detailed information about the way in which keywords relate to each other. The clustering provides a simplified picture by assigning each keyword to a single cluster. Indeed this means that sometimes different items are assigned to different clusters even though the items are linked to each other. The clustering technique used by VOSviewer tries to assign items to clusters in such a way that the number of links between items that are in different clusters is minimized, but there will always be some links that connect items in different clusters.
  • Tanya March 26th, 2018 5:24 pm
    Hi VOSviewer (and thanks for the wonderful support you provide here!),

    I'm trying to launch VOSviewer through the command line to increase available memory. I've downloaded the .jar file and run the code 'java -Xmx1000m -jar VOSviewer.jar' in terminal, however before VOSviewer launches I get a very long error, starting with:

    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at org.pushingpixels.substance.internal.utils.SubstanceColorUtilities.getDefaultBackgroundColor(

    I'm not sure how to proceed from here..? Thanks!
    • Ludo Waltman March 26th, 2018 6:22 pm
      Most likely, this error is caused by the fact that you are using Java version 9. Unfortunately, VOSviewer currently cannot be run using Java version 9. You need to use version 8 of Java. In the future, we of course hope to make VOSviewer compatible with Java version 9, but this requires some significant technical changes to be made to the software.
      • Tanya March 27th, 2018 4:32 pm
        Ah, thanks! I had installed JDK10 in order to run the java command in terminal. I switched to JDK8 and was able to expand the memory with no problems.
  • Antonio February 26th, 2018 2:27 pm
    Hello Ludo.
    I've just updated to new version 6.7, but now I cannot generate the network of authors according to their bibliographical coupling. The option "author" is not avaible anymore, but "documents", "sources", "organizations" and "countries" are still available. When I try to identify the authors by their "documents", all them appear as "anonymous".
    I tested with the same .txt files extracted from Web of Science in the 6.6 version and it worked well.
    Thanks for this powerful software!
    • Antonio February 26th, 2018 2:42 pm
      Just a correction: this problem occurs when I export the results from SciELO Citation Index (a Web of Science collection). But the same .txt file works well with 6.6 version.
      Thanks again!
      • Ludo Waltman February 26th, 2018 3:40 pm
        Could you please send your file to I will then take a look at it. Thanks!
        • Ludo Waltman February 26th, 2018 11:12 pm
          Thanks for sending your file. In VOSviewer 1.6.7, we changed the way in which author data is extracted from Web of Science files. This was done in order to be able to process first names of authors. The new functionality was tested for data downloaded from the Web of Science Core Collection. We did not perform any tests for the Web of Science SciELO citation index. VOSviewer 1.6.7 indeed turns out to be unable to extract author data from Web of Science SciELO files. We were not aware of this, and we will try to fix this problem in the next update of VOSviewer. As a temporary workaround, you could use VOSviewer 1.6.6 for creating maps of authors based on Web of Science SciELO files. Alternatively, in your files, you could change the header 'AU' into 'AF'. By changing the header, VOSviewer 1.6.7 should be able to process your files. Thanks a lot for drawing our attention to this issue.
  • Sven Januszek February 22nd, 2018 2:44 pm
    It seems as if the bug from Scopus has not been fixed yet. I am still facing problems using my CSV files from Scopus. It says: Error while reading Scopus file "XXX" (line: 5974): Incorrect number of coumns.
    • Kirsty February 22nd, 2018 2:51 pm
      Yes it is unfortunately - apparently Scopus have said it should be fixed by the end of the month...
    • Ludo Waltman February 22nd, 2018 5:02 pm
      Indeed the problem has not yet been fixed. The Elsevier Scopus team is still working on it. They expect the problem to be fixed by the end of the month.
      • Ludo Waltman February 23rd, 2018 9:31 am
        I have just been informed by the Elsevier Scopus team that an update of Scopus will take place on Wednesday February 28. This means that on Thursday March 1 the problems with the Scopus CSV export should be solved.
        • Ludo Waltman March 1st, 2018 10:50 am
          I have just performed some tests with the Scopus CSV export. It seems that the problems have been fixed. If anyone is still experiencing problems, then please let me know.
          • Sven March 2nd, 2018 9:28 am
            Seems to still not work for me. I exported the CSV file from Scopus this morning and still get the error message: "Error while reading Scopus file 'XXX' (line 9711): Incorrect number of columns.
            Maybe my excel sheet is just too large with almost 10k rows.
            • Ludo Waltman March 2nd, 2018 9:43 am
              Could you please send your file to me ( Thanks!
              • Sven March 2nd, 2018 9:59 am
                I sent you the files and hope the mail attachment was not too big. Please let me know if you still have not received the mail.
                • Ludo Waltman March 2nd, 2018 4:43 pm
                  Thanks Sven for sending me your files. I have taken a look at them.
                  Scopus has two options for exporting CSV files, an option ‘CSV - Only the first 2,000 documents’ and an option ‘CSV - Export all documents to a CSV file, citation information only’. It seems that you have used the second option, which apparently still suffers from a bug. I will report this to Elsevier. However, my recommendation is to use the first option. Your CSV file will then include more data per document, so that you have more options in VOSviewer for creating maps. It seems that the first option does not suffer from bugs anymore. If you experience any problems with this option, then please let me know.
                  • Sven March 5th, 2018 9:01 am
                    Thanks a lot Ludo!
                    Indeed the first option works out for me. Unfortunately, I would have to use more than just 2000 entries for my analysis. Hopefully, the second option will get fixed soon by Scopus. In case you hear anything from them, it would be nice to get an update from you.
                  • john March 13th, 2018 11:22 am
                    Unfortunately, I'm still not able to generate a map in VOS Viewer based on a Scopus CSV output file. The program reports: Incorrect number of columns. Is this somehow related to the previous reported bug? Or maybe I made a different mistake?
                    Kind regards,
                    • Ludo Waltman March 13th, 2018 12:36 pm
                      I am sorry to hear this, John. Could you please send your file(s) to I will then take a look at them.
Build on Applepie CMS by Waltman Development