VOSviewer Manual. Nees Jan van Eck and Ludo Waltman. 5 December Manual for VOSviewer version 1.5.5

Transcription

1 VOSviewer Manual Nees Jan van Eck and Lud Waltman 5 December 2013 Manual fr VOSviewer versin 1.5.5

2 Table f cntents 1 Intrductin Functinality Main panel Infrmatin panel Overview panel Actin panel Actin tab Items tab Map tab Optins dialg bx File types Map file Netwrk file Thesaurus file Cluster clrs file and scre clrs file Advanced tpics Using cmmand line parameters Making a map available n the internet Increasing the availability f memry References

3 1 Intrductin VOSviewer is a cmputer prgram that can be used fr the fllwing purpses: VOSviewer can be used t create maps based n netwrk data. Maps are created using the VOS mapping technique and the VOS clustering technique. 1 VOSviewer can be used t view and explre maps. It can shw a map in varius different ways, each emphasizing a different aspect f the map. It ffers functinality such as zming, scrlling, and searching, which facilitates the detailed examinatin f a map. The viewing capabilities f VOSviewer are especially useful when wrking with maps cntaining at least a mderately large number f items (e.g., at least 100 r 200 items). VOSviewer is primarily intended t be used fr analyzing biblimetric netwrks. The prgram can fr example be used t create maps f publicatins, authrs, r jurnals based n a citatin, c-citatin, r bibligraphic cupling netwrk r t create maps f keywrds based n a c-ccurrence netwrk. Hwever, the use f VOSviewer is nt restricted t biblimetric netwrks. In fact, VOSviewer can be used t create maps based n any type f netwrk. VOSviewer has been written in the Java prgramming language, which means that it runs n mst hardware and perating system platfrms. VOSviewer can be btained frm the web site The prgram can be used freely fr any purpse. This manual is cncerned with versin f VOSviewer. We explain the functinality f VOSviewer in Chapter 2, and we discuss the file types used by VOSviewer in Chapter 3. Sme advanced tpics are cvered in Chapter 4. Fr additinal infrmatin abut VOSviewer, we refer t a paper that we have written (Van Eck & Waltman, 2010). In this paper, a general intrductin t VOSviewer is prvided. Als, the technical implementatin f specific parts f the prgram is discussed in cnsiderable detail. 1 Tgether, these tw techniques prvide a unified framewrk fr mapping and clustering. Fr mre infrmatin abut the techniques, we refer t Van Eck, Waltman, Dekker, and Van den Berg (2010) and Waltman, Van Eck, and Nyns (2010). 3

4 2 Functinality The main windw f VOSviewer is shwn in Figure 1. As can be seen in the figure, the main windw cnsists f the fllwing fur panels: Main panel. In this panel, a selected area f the currently active map is shwn. The zm and scrll functinality f VOSviewer can be used t select the area f the currently active map that is shwn in the main panel. Infrmatin panel. In this panel, infrmatin abut an item in the currently active map can be shwn. Overview panel. In this panel, an verview f the currently active map is shwn. A rectangular frame is displayed in the verview panel t indicate the area f the currently active map that is shwn in the main panel. Actin panel. This panel can be used t undertake all kinds f actins, such as creating a new map, pening r saving an existing map, making a screensht, changing settings, lcating an item, and cnstructing r transfrming a map. In the next sectins, we discuss each f the panels in mre detail. Figure 1. The main windw f VOSviewer. 4

5 T get sme hands-n experience with VOSviewer, we encurage the reader t use the map file jurnal_map.txt, which is distributed tgether with VOSviewer. This file can be used t reprduce the figures in this chapter. The file cntains a map f 232 jurnals in the fields f ecnmics, management, and peratins research (fr mre details, see Van Eck & Waltman, 2010). T pen the map, press the Open buttn n the Actin tab in the actin panel, select the map file jurnal_map.txt, and press the OK buttn. 2.1 Main panel As can be seen in Figure 1, the main panel f VOSviewer is used t shw a selected area f the currently active map. The zm and scrll functinality f VOSviewer can be used t determine which area f the currently active map is shwn. Depending n the available map data, the main panel cnsists f three r fur tabs. Each tab prvides a different view n the currently active map. We nw discuss each f the tabs: Label View. In the label view, items are indicated by their label and, by default, als by a circle. Fr each item, the fnt size f the item s label and the size f the item s circle depend n the weight f the item. 2 The clr f the circle f an item can be determined in a number f different ways. If items have been assigned t clusters, the clr f the circle f an item can be determined by the cluster t which the item belngs. If scres have been given t items (using the scre clumn in a map file; see Sectin 3.1), the clr f the circle f an item can be determined by the item s scre, where by default clrs range frm blue (scre f 0) t green (scre f 1) t red (scre f 2). 3 A third pssibility is t determine the clr f the circle f an item by the clr f the item as specified in a map file (using the red, green, and blue clumns; see Sectin 3.1). The Item clrs drp dwn list in the Optins dialg bx (see Subsectin 2.4.4) can be used t chse between the different ways f clring items. By default, t avid verlapping labels, nly a subset f all labels is 2 The weight f an item is determined by the weight r nrmalized weight clumn in a map file (see Sectin 3.1). When a new map is created withut prviding a map file with a weight r nrmalized weight clumn, the weight f an item is set equal t the ttal strength f all links f the item. When an existing map is pened withut prviding a map file with a weight r nrmalized weight clumn, all items in the map are given the same weight. 3 If clrs are determined by the scres f items, a clr bar is shwn in the lwer right crner f the main panel. This clr bar indicates which clrs crrespnd with which scres. By clicking n the clr bar, it is pssible t imprt an alternative clr scheme frm a scre clrs file (see Sectin 3.4). 5

6 visible in the label view. Als, by default, n lines between items are displayed. Hwever, this can be changed in the Optins dialg bx. The label view is particularly useful fr detailed examinatins f a map. An example f the label view is shwn in Figure 2. Density View. In the density view, items are indicated by their label in a similar way as in the label view. Each pint in a map has a clr that depends n the density f items at that pint. By default, this clr is smewhere in between red and blue. The larger the number f items in the neighbrhd f a pint and the higher the weights f the neighbring items, the clser the clr f the pint is t red. Cnversely, the smaller the number f items in the neighbrhd f a pint and the lwer the weights f the neighbring items, the clser the clr f the pint is t blue. The density view is particularly useful t get a quick verview f the imprtant areas f a map. We refer t Van Eck and Waltman (2010) fr a detailed discussin f the technical implementatin f the density view. An example f the density view is shwn in Figure 3. Cluster Density View. The cluster density view is available nly if items have been assigned t clusters. The cluster density view is similar t the rdinary density view except that the density f items is displayed separately fr each cluster f items. In the cluster density view, the clr f a pint in a map is clse t the clr f a certain cluster if there are a large number f items belnging t that cluster in the neighbrhd f the pint. Like in the rdinary density view, items with high weights cunt mre heavily than items with lw weights. The cluster density view is particularly useful t get a quick verview, fr each cluster separately, f the imprtant areas f a map. We refer t Van Eck and Waltman (2010) fr a detailed descriptin f the technical implementatin f the cluster density view. An example f the cluster density view is shwn in Figure 4. Scatter View. In the scatter view, items are indicated by a small circle. Items are clred in the same way as in the label view. N labels are displayed in the scatter view. By default, lines between items are nt displayed either, but this can be changed in the Optins dialg bx. The scatter view can be useful t get an verview f the general structure f a map. An example f the scatter view is shwn in Figure 5. 6

7 Figure 2. The label view. Figure 3. The density view. 7

8 Figure 4. The cluster density view. Figure 5. The scatter view. 8

9 T facilitate the detailed examinatin f a map, VOSviewer ffers zm and scrll functinality. In the main panel, zming and scrlling can be dne in the fllwing three ways: Using the muse. T zm in, mve the muse upwards while keeping the right muse buttn pressed. Cnversely, t zm ut, mve the muse dwnwards while keeping the right muse buttn pressed. As an alternative, the muse wheel can be used t zm in and ut. T scrll thrugh a map, mve the muse while keeping the left muse buttn pressed. Using the navigatin buttns in the upper right crner f the main panel (see Figure 1). Use the plus and minus buttns t zm in and ut. Use the arrw buttns t scrll thrugh a map. Using the keybard. Use the plus and minus keys t zm in and ut. Use the arrw keys t scrll thrugh a map. 2.2 Infrmatin panel In the infrmatin panel f VOSviewer, infrmatin abut an item in the currently active map can be shwn. Fr example, when ne mves the muse cursr ver the label f an item in the main panel, infrmatin abut the item will be shwn in the infrmatin panel. If item descriptins have been prvided (using the descriptin clumn in a map file; see Sectin 3.1), the descriptin f the item will be shwn. If n item descriptins have been prvided, the label f the item will be shwn alng with the number f the cluster t which the item belngs and the scre f the item (assuming that items have been assigned t clusters and that scres have been given t items). Infrmatin abut a link between tw items can als be shwn in the infrmatin panel. This is pssible nly if lines are displayed in the main panel. When ne mves the muse cursr ver the line between tw items, infrmatin abut the link between the items will be shwn in the infrmatin panel. The labels f the items and the strength f the link will be shwn. The height f the infrmatin panel can be adjusted. This can be dne by dragging the area between the infrmatin panel and the main panel using the muse. 2.3 Overview panel In the verview panel f VOSviewer, an verview f the currently active map is shwn. Each item in the map is indicated by a small clred dt. A rectangular frame is displayed in the verview panel t indicate the area f the currently active 9

10 map that is shwn in the main panel. By left-clicking in the verview panel, the area f the currently active map that is shwn in the main panel can be changed. 2.4 Actin panel The actin panel f VOSviewer can be used t undertake all kinds f actins. The panel cnsists f three tabs: The Actin tab, the Items tab, and the Map tab. These tabs are discussed in Subsectins 2.4.1, 2.4.2, and In Subsectin 2.4.4, the Optins dialg bx is discussed Actin tab The Actin tab can be used t perfrm a number f basic actins. The fllwing buttns are available n the Actin tab: Map. Create. Use this buttn t create a new map. The buttn brings up the Create Map wizard. There are tw ways in which a new map can be created using this wizard: Create a map based n a netwrk. This ptin requires the adjacency matrix f a netwrk. The adjacency matrix indicates which pairs f items in the netwrk are linked t each ther, and fr each pair f linked items it indicates the strength f their link. The matrix can be read frm a netwrk file. In additin t a netwrk file, ne may als prvide a map file. The map file may fr example cntain labels and descriptins f items. We refer t Sectins 3.1 and 3.2 fr a detailed discussin f map files and netwrk files. Instead f a map file and a netwrk file, it is als pssible t use Pajek files. 4 A third pssibility is t use a Web f Science file. 5 The use f Web f Science files allws ne t easily create maps f scientific publicatins, scientific jurnals, researchers, r research rganizatins based n either c-citatin relatins (i.e., multiple items being cited by the same publicatin) r 4 Pajek is a well-knwn cmputer prgram fr scial netwrk analysis (De Ny, Mrvar, & Batagelj, 2011). It is available at VOSviewer supprts Pajek matrix, netwrk, partitin, and vectr files. 5 Web f Science is a majr bibligraphic database f scientific publicatins prduced by Thmsn Reuters. It cntains bibligraphic data n publicatins frm mre than 10,000 jurnals in the sciences, scial sciences, arts, and humanities. Web f Science is available at A subscriptin is required. 10

11 bibligraphic cupling relatins (i.e., multiple items citing the same publicatin). Create a map based n a text crpus. 6 This ptin requires a text crpus. The crpus is stred in a crpus file. A crpus file is a text file that cntains n each line the text f a dcument. This text is assumed t be in English. Using natural language prcessing techniques, VOSviewer extracts terms frm the crpus file, where a term is defined as a sequence f nuns and adjectives (ending with a nun). Based n the extracted terms, VOSviewer creates a term map. This is a map in which terms are lcated in such a way that the distance between tw terms prvides an indicatin f the number f c-ccurrences f the terms. In general, the smaller the distance between tw terms, the larger the number f c-ccurrences f the terms. Tw terms are said t c-ccur if they bth ccur n the same line in the crpus file. In additin t a crpus file, ne may als prvide a scres file. A scres file is a text file that cntains n each line the scre f a dcument. By default, it is expected that mst scres are in the range between 0 and 2. Based n the scres in a scres file, VOSviewer calculates a scre fr each term in the term map. The scre f a term equals the average scre f the dcuments in which the term ccurs. In the label view, clrs can be used t indicate the scres f terms (see Sectin 2.1). It is als pssible t create a term map based n a Web f Science r Scpus file 7 instead f a crpus file. In that case, terms are extracted frm the titles and abstracts f scientific publicatins. Open. Use this buttn t pen an existing map. The buttn brings up the Open Map dialg bx. Map data can be read frm a map file. The map file must cntain crdinates f items. The file may als cntain, fr example, labels, descriptins, weights, and cluster numbers f items. In additin t a map file, ne may als prvide a netwrk file. The netwrk file cntains the adjacency matrix f a netwrk. Based n this matrix, lines can be displayed between the items in a map. Instead f a map file and a netwrk file, it is als pssible t use Pajek files. Fr a detailed discussin f map files and netwrk files, we refer t Sectins 3.1 and We refer t Van Eck and Waltman (2011) fr mre infrmatin abut this ptin. 7 Like Web f Science, Scpus is a majr bibligraphic database f scientific publicatins. Scpus is prduced by Elsevier and is available at A subscriptin is required. 11

12 Save. This split buttn ffers three ptins: Save map. This ptin is the default chice. Chse this ptin t save the currently active map in a map file. Map files are discussed in Sectin 3.1. Instead f a map file, it is als pssible t use a Pajek file. Save netwrk. This ptin can be chsen nly if the adjacency matrix f a netwrk is available. Chse this ptin t save the adjacency matrix in a netwrk file. Netwrk files are discussed in Sectin 3.2. Instead f a netwrk file, it is als pssible t use a Pajek file. Save nrmalized netwrk. This ptin can be chsen nly if the adjacency matrix f a netwrk is available. Chse this ptin t save the nrmalized adjacency matrix in a netwrk file. Nrmalizatin f an adjacency matrix is discussed in Subsectin Netwrk files are discussed in Sectin 3.2. Instead f a netwrk file, it is als pssible t use a Pajek file. Print. Use this buttn t print a screensht f the main panel. Screensht. This split buttn ffers tw ptins: Save t file. This ptin is the default chice. Chse this ptin t save a screensht f the main panel. The screensht resembles the main panel as clsely as pssible. Hwever, the navigatin buttns in the upper right crner f the main panel are nt shwn in the screensht. If the Optimize labeling check bx in the Screensht Optins dialg bx (see belw) is checked, the number f labels visible in the screensht is ptimized. This means that sme labels nt visible in the main panel may be visible in the screensht. Screenshts can be saved in a number f graphic file frmats. Fr mst applicatins, we recmmend the PNG frmat. Sme frmats, such as EPS, PDF, and SVG, use vectr graphics when saving a screensht. This has the advantage that the screensht can be resized withut lss f quality. We nte that Figures 2 t 5 were btained using the screensht functinality f VOSviewer. Cpy t clipbard. Chse this ptin t cpy a screensht f the main panel t the clipbard. The screensht can fr example be pasted int a Wrd dcument r a PwerPint presentatin. Screensht ptins. Chse this ptin t bring up the Screensht Optins dialg bx. This dialg bx can be used t change sme 12

13 screensht-related settings f VOSviewer. The Scaling drp dwn list determines the reslutin (i.e., the number f pixels) f a screensht. The reslutin is calculated relative t the reslutin f the main panel. Using the default scaling f 100%, screenshts have the same reslutin as the main panel. Using fr example a scaling f 200%, screenshts have a reslutin that is twice as high (i.e., twice as many pixels hrizntally and vertically) as the reslutin f the main panel. The Scaling drp dwn list has n effect n screenshts that are saved in a file frmat that uses vectr graphics. The Optimize labeling check bx determines whether the number f labels visible in a screensht is ptimized. Optimizing the number f labels visible in a screensht means that sme labels nt visible in the main panel itself may be visible in a screensht f the main panel. The Optimize labeling check bx has n effect if the N verlap check bx in the Optins dialg bx (see Subsectin 2.4.4) is unchecked. The Include brder check bx determines whether a brder is included arund a screensht. Optins/Inf. Optins. This buttn brings up the Optins dialg bx. This dialg bx can be used t change varius settings f VOSviewer. The Optins dialg bx is discussed in Subsectin Manual. Use this buttn t pen the VOSviewer manual. This requires an internet cnnectin. Abut VOSviewer. This split buttn ffers tw ptins: Abut VOSviewer. This ptin brings up the Abut VOSviewer dialg bx. This dialg bx prvides sme general infrmatin abut VOSviewer, such as the versin number, a cpyright ntice, a license text, the address f the VOSviewer web site, and a list f sftware libraries used by VOSviewer. Check fr updates. Chse this ptin t check whether a new versin f VOSviewer is available. This requires an internet cnnectin Items tab The Items tab prvides a list f items in the currently active map. By default, a list f all items in the map is prvided. Hwever, a filter can be used t restrict the list t a subset f the items in the map. T d s, enter a filter string in the Filter text bx. This yields a list f all items whse label cntains the filter string. 13

14 The Grup items by cluster check bx determines the way in which items are listed. If the check bx is unchecked, items are simply listed alphabetically. If the check bx is checked, items are first gruped by cluster and then listed alphabetically within each cluster. By duble-clicking n an item n the Items tab, the item is shwn in the main panel Map tab The Map tab can be used t cnstruct r transfrm a map. Maps are cnstructed using the VOS mapping technique and the VOS clustering technique. 8 The Map tab can als be used t change the parameters f these techniques. The fllwing parameters and cntrls are available n the Map tab: Parameters. Clustering reslutin. This parameter determines the level f detail prvided by the VOS clustering technique. The parameter must have a nnnegative value. The larger the value f the parameter, the larger the number f clusters that will be btained. Our recmmendatin is t try ut different values fr the parameter and t use the value that yields the level f detail cnsidered mst satisfactry fr the particular applicatin at hand. Min. cluster size. This parameter determines the minimum cluster size used by the VOS clustering technique. Each cluster prduced by the VOS clustering technique must cnsist f the minimum number f items specified by this parameter. The Min. cluster size parameter can be useful t simplify the clustering slutins btained frm the VOS clustering technique by getting rid f small and uninteresting clusters. Advanced Parameters. This buttn brings up the Advanced Parameters dialg bx. This dialg bx can be used t change a number f mre advanced parameters f the VOS mapping and clustering techniques. These parameters are discussed belw. Run. The Run buttn is available nly after a new map has been created (using the Create buttn n the Actin tab in the actin panel). The buttn can be used t run the VOS mapping and clustering techniques. The ptin buttns determine whether bth techniques are run r nly ne f them. 8 We refer t Van Eck et al. (2010), Waltman and Van Eck (2013), and Waltman et al. (2010) fr mre infrmatin abut these techniques. 14

15 Rtate/flip. Rtate. Use this buttn t rtate the currently active map. The Degrees t rtate parameter determines the number f degrees by which the map will be rtated. Flip Hrizntally. Use this buttn t flip the currently active map in hrizntal directin. Flip Vertically. Use this buttn t flip the currently active map in vertical directin. As mentined abve, the Advanced Parameters dialg bx can be used t change a number f mre advanced parameters f the VOS mapping and clustering techniques. The fllwing parameters are available: Nrmalizatin. Methd. This parameter determines the methd that is used t nrmalize the adjacency matrix f a netwrk. There are three ptins: N nrmalizatin. Using this ptin, n nrmalizatin is perfrmed. In general, we d nt recmmend this ptin. Nrmalizatin methd 1. This is the default nrmalizatin methd. This methd uses the s-called assciatin strength measure (Van Eck & Waltman, 2009). Nrmalizatin methd 2. This is an alternative nrmalizatin methd. The difference between this methd and the default methd is smewhat technical, and we will therefre nt discuss it here. Ignre self links. This parameter determines whether self links in a netwrk are ignred. In ther wrds, the parameter determines whether the main diagnal f the adjacency matrix f a netwrk is ignred. If self links are ignred, the elements n the main diagnal f the adjacency matrix are set equal t zer. In general, we recmmend t ignre self links. Randm number generatr. Use seed based n current time. This check bx determines whether the randm number generatr used by the ptimizatin algrithms f the VOS mapping and clustering techniques has a fixed seed r a seed that is based n the current time. In the latter case, each time the VOS mapping and clustering techniques are run, a different seed will be used, pssibly leading t different results. Using a fixed seed, n the ther hand, the same results 15

16 will be btained each time the VOS mapping and clustering techniques are run. Use fixed seed. This text bx determines the seed f the randm number generatr used by the ptimizatin algrithms f the VOS mapping and clustering techniques. The seed must be a nn-negative integer. The Use fixed seed text bx is available nly if the Use seed based n current time check bx is unchecked. Mapping. Randm starts. This parameter determines the number f times the ptimizatin algrithm f the VOS mapping technique is run. Each time the ptimizatin algrithm is run, a smewhat different mapping slutin may be btained. The best mapping slutin btained in all runs f the ptimizatin algrithm will be used as the final mapping slutin. The larger the value f the Randm starts parameter, the mre accurate the final mapping slutin that will be btained. Cnvergence. This parameter determines the cnvergence criterin used by the ptimizatin algrithm f the VOS mapping technique. The parameter must have a value between 0 and The clser the value f the parameter is t zer, the mre accurate the mapping slutin that will be btained. In general, the default value f the parameter wrks well and des nt need t be changed. Max. iteratins. This parameter determines the maximum number f iteratins perfrmed by the ptimizatin algrithm f the VOS mapping technique. The larger the value f the parameter, the mre accurate the mapping slutin that will be btained. In general, the default value f the parameter wrks well and des nt need t be changed. Clustering. Randm starts. This parameter determines the number f times the ptimizatin algrithm f the VOS clustering technique is run. Each time the ptimizatin algrithm is run, a smewhat different clustering slutin may be btained. The best clustering slutin btained in all runs f the ptimizatin algrithm will be used as the final clustering slutin. The larger the value f the Randm starts parameter, the mre accurate the final clustering slutin that will be btained. 16

17 Iteratins. This parameter determines the number f iteratins perfrmed by the ptimizatin algrithm f the VOS clustering technique. The larger the value f the parameter, the mre accurate the clustering slutin that will be btained. In general, the default value f the parameter wrks well and des nt need t be changed Optins dialg bx The Optins dialg bx can be used t change varius settings f VOSviewer. The fllwing settings can be changed: Labels. Size. This slider determines the fnt size used t display the labels f items in the main panel. Size variatin. The higher the weight f an item, the larger the fnt that is used t display the item s label in the main panel. The Size variatin slider determines the strength f this effect. Max. length. This text bx determines the maximum length f a label displayed in the main panel. If the length f a label exceeds the maximum length, the last part f the label is nt displayed. N verlap. This check bx determines whether labels are allwed t verlap each ther in the main panel. If verlapping labels are nt allwed, it depends n items weights which labels are displayed and which are nt. A label f an item with a higher weight has pririty ver a label f an item with a lwer weight. Blurred backgrund. This check bx determines whether a s-called blurred backgrund is used in the main panel. Using a blurred backgrund, labels that are nt displayed in the rdinary way (due t verlap with ther labels) are displayed in a blurred way. The Blurred backgrund check bx has an effect nly if the N verlap check bx is checked. Gradual appearance. This check bx determines whether in the main panel labels appear gradually r instantaneusly when ne zms in. The Gradual appearance check bx has an effect nly if the N verlap check bx is checked. Lines. Number f lines. If the adjacency matrix f a netwrk is available, lines can be displayed in the label view and the scatter view f the main panel. 17

18 Lines can be displayed between any pair f items with a nn-zer link strength. The Number f lines text bx determines the maximum number f lines t be displayed. If the number f links with a nn-zer strength exceeds the maximum number f lines t be displayed, lines are displayed nly fr the strngest links. Use nrmalizatin. This check bx determines whether lines are displayed based n nrmalized r unnrmalized link strengths. In general, the use f unnrmalized link strengths yields mre satisfactry results. Visualizatin. Item clrs. Use this drp dwn list t chse the way in which items are clred in the label view and the scatter view and in the verview panel. The fllwing ptins may be available: N item clrs. All items are clred in gray. Cluster clrs. Items are clred based n the cluster t which they belng. As discussed belw, cluster clrs can be chsen in the Chse Cluster Clrs dialg bx. The Cluster clrs ptin is available nly if items have been assigned t clusters. Scre clrs. Items are clred based n their scre, with clrs by default ranging frm blue (scre f 0) t green (scre f 1) t red (scre f 2). The Scre clrs ptin is available nly if scres have been given t items (using the scre clumn in a map file; see Sectin 3.1). User defined clrs. Each item has its wn clr as specified in a map file (using the red, green, and blue clumns; see Sectin 3.1). Label view. Use this drp dwn list t chse the visualizatin used in the label view. The fllwing ptins are available: Shw labels nly. Items are indicated nly by their label. Shw labels and circles. Items are indicated bth by their label and by a circle. Shw labels and frames. Items are indicated by their label displayed within a rectangular frame. Density view kernel width. This slider determines the value f the kernel width parameter f the density view and the cluster density view. 18

19 Density view transfrmatin. This slider determines the value f the clr transfrmatin parameter f the density view and the cluster density view. 9 Density view clr scheme. Use this drp dwn list t chse the clr scheme used in the density view. White backgrund in cluster density view. This check bx determines whether a black r a white backgrund clr is used in the cluster density view. Chse Cluster Clrs. This buttn is available nly if items have been assigned t clusters. The buttn brings up the Chse Cluster Clrs dialg bx. This dialg bx can be used t chse the clrs f clusters. Cluster clrs can als be imprted frm r exprted t a cluster clrs file (see Sectin 3.4). 9 We refer t Van Eck and Waltman (2010) fr mre infrmatin abut the kernel width parameter and the clr transfrmatin parameter. 19

20 3 File types The tw primary file types used by VOSviewer are the map file and the netwrk file. Map files and netwrk files are simple text files that can easily be viewed and edited using a text editr (e.g., Ntepad) r a spreadsheet prgram (e.g., Excel). Map files and netwrk files cnsist f multiple clumns. Hence, each line in a map file r a netwrk file cntains multiple pieces f infrmatin. Different pieces f infrmatin n the same line are separated frm each ther by a cmma, a semicln, r a tab. If a piece f infrmatin (e.g., the label f an item) itself cntains a cmma r a semicln, the whle piece f infrmatin needs t be enclsed within duble qutes. We discuss map files and netwrk files in mre detail in Sectins 3.1 and 3.2. Three additinal file types, the thesaurus file, the cluster clrs file, and the scre clrs file, are discussed in Sectins 3.3 and 3.4. We nte that all example files mentined in this chapter are distributed tgether with VOSviewer. 3.1 Map file A map file is a text file that cntains infrmatin abut the items in a map. Each line in a map file crrespnds with an item. The nly exceptin is the first line. This is a header line that indicates what is cntained in each f the clumns f a map file. Belw, we list the clumns that can be used in a map file. Fr each clumn, we prvide the clumn header and we specify what the clumn cntains. id label sublabel descriptin url x y weight The ID f an item. Items need t have an ID nly if a map file is used in cmbinatin with a netwrk file. The label f an item. The sublabel f an item. In the main panel, the sublabel f an item is displayed belw the item s rdinary label. Sublabels are displayed in a smaller fnt. The descriptin f an item. The descriptin f an item is used t prvide infrmatin abut the item in the infrmatin panel. HTML frmatting can be used in this clumn. The URL f an item. This clumn can be used t assciate a web page with an item. When ne clicks n the label f an item in the main panel, the web page assciated with the item will be pened in a web brwser. The hrizntal crdinate f an item. The vertical crdinate f an item. The weight f an item. Only nn-negative numbers are allwed in this clumn. The higher the weight f an item, the mre prminent the item is presented in the 20

21 main panel. nrmalized weight scre cluster red The nrmalized weight f an item. Only nn-negative numbers are allwed in this clumn. The higher the nrmalized weight f an item, the mre prminent the item is presented in the main panel. The default presentatin f an item is btained by setting the item s nrmalized weight t 1. The scre f an item. In the main panel and the verview panel, items can be clred based n their scres, with by default clrs ranging frm blue (scre f 0) t green (scre f 1) t red (scre f 2). The number f the cluster t which an item belngs. Only integers between 1 and 1000 are allwed in this clumn. The red cmpnent f the clr f an item. Only integers between 0 and 255 are allwed in this clumn. green The green cmpnent f the clr f an item. Only integers between 0 and 255 are allwed in this clumn. blue The blue cmpnent f the clr f an item. Only integers between 0 and 255 are allwed in this clumn. In a map file, ne always uses nly a subset f the abve clumns. The rder in which the clumns are used is nt imprtant. There are a number f restrictins n the clumns that are used in a map file: There must be an id clumn r a label clumn. (If there is n label clumn, the ID f an item is used as the item s label.) If there is a sublabel clumn, there must be a label clumn as well. The x and y clumns must be used tgether. The red, green, and blue clumns must be used tgether. The weight clumn and the nrmalized weight clumn cannt be used tgether. Fr an example f a map file, see the file jurnal_map.txt. 3.2 Netwrk file A netwrk file is a text file that cntains the adjacency matrix f a netwrk. The adjacency matrix f a netwrk is a square matrix that indicates fr each pair f items in the netwrk the strength f the link between the items. The strength f a link is given by a nn-negative number. If there is n link between tw items, the strength f the link between the items equals zer. VOSviewer wrks with symmetric adjacency matrices. If a netwrk file cntains an asymmetric adjacency matrix, VOSviewer will make the matrix symmetric by averaging crrespnding elements n bth sides f the main diagnal. 21

22 A netwrk file has either a full frmat r a sparse frmat: Full frmat. The entire adjacency matrix, including elements that are equal t zer, is stred in the netwrk file. The file cnsists f n lines and n + 1 clumns, where n dentes the number f items in the netwrk. The element in the ith rw and the jth clumn f the adjacency matrix is stred n the ith line and in the (j + 1)th clumn f the netwrk file. The first clumn f the netwrk file cntains IDs f items. This clumn indicates fr each rw and clumn f the adjacency matrix the ID f the crrespnding item. Fr an example f a netwrk file in full frmat, see the file jurnal_netwrk_full.txt. Sparse frmat. Only the nn-zer elements f the adjacency matrix are stred in the netwrk file. The file cnsists f tw r three clumns. The first tw clumns cntain IDs f items. The third clumn cntains the nn-zer elements f the adjacency matrix. This clumn indicates the strength f the link between the items referred t in the first tw clumns. If there is n third clumn, the strength f the link between the items referred t in the first tw clumns always equals ne. In the case f a symmetric adjacency matrix, it is sufficient t stre nly half f the matrix (either the upper triangular part r the lwer triangular part) in the netwrk file. Fr an example f a netwrk file in sparse frmat, see the file jurnal_netwrk_sparse.txt. A netwrk file is usually used in cmbinatin with a map file. Fr each item ID in the netwrk file, there must then be a crrespnding item ID in the map file. 3.3 Thesaurus file A thesaurus file is a text file that can be used in the fllwing situatins: When creating a map based n a Web f Science file (see Subsectin 2.4.1), a thesaurus file can be used t merge different variants f a surce title, an authr name, an rganizatin name, r a cited reference. This may fr example be useful when the name f a researcher is written in different ways in different publicatins (e.g., with first initial nly and with all initials). A thesaurus file can then be used t indicate that different names in fact refer t the same researcher. When creating a map based n a crpus file (see Subsectin 2.4.1), a thesaurus file can be used t merge synnyms int a single term. This may be useful nt nly fr merging different terms referring t the same cncept, but als fr merging different spellings f the same term (e.g., behavir and 22

23 behaviur). It may als be useful fr merging an abbreviatin f a term with the term itself. Each line in a thesaurus file cntains a label and indicates an alternative label that replaces the riginal label. The nly exceptin is the first line. This is a header line that indicates what is cntained in each f the clumns f a thesaurus file. A thesaurus file must have tw clumns: A label clumn and a replace by clumn. The label clumn cntains a label. Depending n the situatin (see abve), a label may represent a surce title, an authr name, an rganizatin name, a cited reference, r a term. The replace by clumn cntains an alternative label that replaces the riginal label. The replace by clumn may als be empty. In that case, the riginal label is nt replaced by an alternative ne, but instead the riginal label is simply ignred. When creating a map based n a crpus file, this allws ne t use a thesaurus file as a kind f stp wrd list. A thesaurus file may fr example indicate that certain uninteresting terms (e.g., cpyright and Elsevier in the case f a crpus f abstracts f scientific publicatins) shuld be ignred. Fr examples f thesaurus files, see the files thesaurus_authrs.txt and thesaurus_terms.txt. 3.4 Cluster clrs file and scre clrs file A cluster clrs file is a text file that cntains the clrs f clusters. Each line in a cluster clrs file crrespnds with a cluster. The nly exceptin is the first line. This is a header line that indicates what is cntained in each f the clumns f a cluster clrs file. A cluster clrs file must have fur clumns: A cluster clumn, a red clumn, a green clumn, and a blue clumn. The cluster clumn cntains cluster numbers. Only integers between 1 and 1000 are allwed in this clumn. The red, green, and blue clumns cntain the red, green, and blue cmpnents f the clrs f clusters. Only integers between 0 and 255 are allwed in these clumns. Fr an example f a cluster clrs file, see the file cluster_clrs.txt. A scre clrs file is similar t a cluster clrs file except that the clrs it cntains crrespnd with scres rather than with clusters. This means that instead f a cluster clumn a scre clrs file has a scre clumn. If scres have been given t items (using the scre clumn in a map file; see Sectin 3.1), items can be clred by matching their scres with the scres in the scre clumn f the scre clrs file. Exact matching f scres is usually nt pssible, and in that case the clrs in the scre clrs file are interplated. Fr an example f a scre clrs file, see the file scre_clrs.txt. 23

24 4 Advanced tpics In this chapter, sme advanced tpics are addressed. We first cnsider the use f cmmand line parameters (Sectin 4.1). We then discuss hw a map can be made available n the internet (Sectin 4.2) and hw the amunt f memry available t VOSviewer can be increased (Sectin 4.3). 4.1 Using cmmand line parameters VOSviewer supprts a number f cmmand line parameters. These parameters can fr example be used t autmatically pen a map when VOSviewer is started r t verride sme f the default settings f VOSviewer. The cmmand line parameters supprted by VOSviewer are listed belw. Cmmand line parameters fr pening r creating a map based n a map file and/r a netwrk file map netwrk Use this parameter t specify a map file (see Sectin 3.1). The map in this file will be pened when VOSviewer is started. Use this parameter t specify a netwrk file (see Sectin 3.2). An adjacency matrix will be read frm this file when VOSviewer is started. The adjacency matrix can be used t display lines between the items in a map r t create a new map. Cmmand line parameters fr pening r creating a map based n ne r mre Pajek files pajek_netwrk pajek_partitin pajek_vectr Use this parameter t specify a Pajek netwrk (r matrix) file. Based n this file, a map will be pened r created when VOSviewer is started. Use this parameter t specify a Pajek partitin file. Cluster numbers f items will be read frm this file when VOSviewer is started. Use this parameter t specify a Pajek vectr file. Weights f items will be read frm this file when VOSviewer is started. Cmmand line parameters fr creating a term map based n a crpus file crpus cunting_methd min_n_ccurrences n_terms Use this parameter t specify a crpus file. Based n this file, a term map will be created when VOSviewer is started. Use this parameter t specify the cunting methd t be used in the creatin f the term map (1 fr binary cunting and 2 fr full cunting). Use this parameter t specify the minimum number f ccurrences a term must have t be included in the term map. Use this parameter t specify the number f terms t be included in the term map. VOSviewer will select the terms that seem mst relevant. 24

25 scres thesaurus Use this parameter t specify a scres file. In the creatin f the term map, this file will be used t calculate a scre fr each term. Use this parameter t specify a thesaurus file (see Sectin 3.3). In the creatin f the term map, this file will be used t merge synnyms int a single term. Other cmmand line parameters cluster_clrs encding file_lcatin label_size label_size_variatin n_lines n_clustering scre_clrs view view_nly zm_level Use this parameter t specify a cluster clrs file (see Sectin 3.4). Cluster clrs will be imprted frm this file when VOSviewer is started. Cluster clrs can be used nly if items have been assigned t clusters. Use this parameter t specify the character encding that is used by VOSviewer t read and write text files. Fr a list f the available encdings, see If this parameter is nt used, VOSviewer will attempt t autmatically determine the crrect encding when reading a text file (which in sme cases may result in the use f an incrrect encding), while it will use the default encding when writing a text file. Use this parameter t specify the flder that is used by VOSviewer as the default file lcatin. Use this parameter t specify the initial value f the Size slider in the Optins dialg bx (see Subsectin 2.4.4). Use this parameter t specify the initial value f the Size variatin slider in the Optins dialg bx (see Subsectin 2.4.4). Use this parameter t specify the initial value f the Number f lines text bx in the Optins dialg bx (see Subsectin 2.4.4). Use this parameter t indicate that n clustering must be perfrmed when VOSviewer is started. This parameter can fr example be used tgether with the pajek_netwrk parameter. A map will then be pened r created based n a Pajek netwrk file, but n clustering f the items in the map will be perfrmed. Use this parameter t specify a scre clrs file (see Sectin 3.4). Scre clrs will be imprted frm this file when VOSviewer is started. Scre clrs can be used nly if scres have been given t items (using the scre clumn in a map file; see Sectin 3.1). Use this parameter t specify which tab in the main panel will be selected when VOSviewer is started (1 fr the Label View tab, 2 fr the Density View tab, 3 fr the Cluster Density View tab, and 4 fr the Scatter View tab). Use this parameter t start VOSviewer in the view nly mde. In this mde, the Run buttn n the Map tab in the actin panel is nt available. Use this parameter t specify the initial zm level in the main panel. The zm level must have a value f at least 1. The higher the zm level, the mre the main panel will be zmed in n the center f a map. 25

26 T use the abve cmmand line parameters, VOSviewer needs t be run frm the cmmand line. When using the Windws executable f VOSviewer, 10 this can fr example be dne as fllws: VOSviewer map jurnal_map.txt view 2 zm_level 2.5 In this way, VOSviewer will be started and the map in the map file jurnal_map.txt will be pened. Als, the Density View tab in the main panel will be selected, and the main panel will be zmed in n the center f the map. When instead f the Windws executable f VOSviewer the VOSviewer JAR file is used, VOSviewer can fr example be run in the fllwing way: java jar VOSviewer.jar map jurnal_map.txt view 2 zm_level 2.5 We nte that sme cmmand line parameters cannt be used tgether. Fr example, the map and pajek_netwrk parameters and the map and crpus parameters cannt be used tgether. On the ther hand, sme parameters can nly be used in cmbinatin with anther parameter. The pajek_partitin parameter fr example can nly be used in cmbinatin with the pajek_netwrk parameter. Similarly, the cunting_methd parameter can nly be used in cmbinatin with the crpus parameter. 4.2 Making a map available n the internet Suppse ne wants t make a map available n the internet. One way t d this is simply by making a map file and a netwrk file (r nly a map file) available n the internet. T pen the map, ne then needs t take tw steps. In the first step, the map file and the netwrk file are dwnladed frm the internet. In the secnd step, VOSviewer is started and the dwnladed map file and netwrk file are used t pen the map. The abve tw-step apprach is nt very cnvenient, and therefre an alternative apprach is available as well. In this alternative apprach, a map can be pened in VOSviewer directly frm a web page. The alternative apprach wrks as fllws. A map file and a netwrk file (r nly a map file) need t be made available n the internet. Suppse these files are lcated at and 10 The Windws executable f VOSviewer is available at The VOSviewer JAR file can be btained here as well. 26

27 The map can then be made available n a web page by creating a hyperlink that pints t txt&netwrk= Using this hyperlink, the map can be pened directly in VOSviewer. We nte that all cmmand line parameters discussed in Sectin 4.1 can als be used in a hyperlink. Fr example, t pen a map, t g directly t the density view, and t zm in n the center f the map, the fllwing hyperlink can be used: txt&netwrk= 4.3 Increasing the availability f memry When using VOSviewer t wrk with large maps (e.g., maps cntaining several thusands f items), the memry requirements can be quite substantial. VOSviewer will prduce an ut f memry errr if there is nt enugh memry available. The availability f memry can be increased by running the VOSviewer JAR file frm the cmmand line and specifying the amunt f memry that needs t be available. Fr example, if 1000 MB f memry needs t be available, the VOSviewer JAR file can be run as fllws: java -Xmx1000m -jar VOSviewer.jar When wrking with large maps, VOSviewer may als prduce a stack verflw errr. T prevent this errr frm ccurring, the stack size needs t be increased. This can be dne by running the VOSviewer JAR file frm the cmmand line in the fllwing way: java -Xss1000k -jar VOSviewer.jar In this case, the stack size is set t 1000 KB, but ther values are pssible as well. 27

28 References De Ny, W., Mrvar, A., & Batagelj, V. (2011). Explratry scial netwrk analysis with Pajek (2nd ed.). Cambridge University Press. Van Eck, N.J., & Waltman, L. (2009). Hw t nrmalize cccurrence data? An analysis f sme well-knwn similarity measures. Jurnal f the American Sciety fr Infrmatin Science and Technlgy, 60(8), Van Eck, N.J., & Waltman, L. (2010). Sftware survey: VOSviewer, a cmputer prgram fr biblimetric mapping. Scientmetrics, 84(2), Van Eck, N.J., & Waltman, L. (2011). Text mining and visualizatin using VOSviewer. ISSI Newsletter, 7(3), Van Eck, N.J., Waltman, L., Dekker, R., & Van den Berg, J. (2010). A cmparisn f tw techniques fr biblimetric mapping: Multidimensinal scaling and VOS. Jurnal f the American Sciety fr Infrmatin Science and Technlgy, 61(12), Waltman, L., & Van Eck, N.J. (2013). A smart lcal mving algrithm fr largescale mdularity-based cmmunity detectin. Eurpean Physical Jurnal B, 86, 471. Waltman, L., Van Eck, N.J., & Nyns, E.C.M. (2010). A unified apprach t mapping and clustering f biblimetric netwrks. Jurnal f Infrmetrics, 4(4),