Just below the surface.

Using Gephi("an interactive visualization and exploration platform for all kinds of networks") to create unprocessed maps of exposed keywords to the user in the library of the Peace Palace, will result in an image in which a few huge subjects will dominate. These subjects are indicators of the core business of the library: Human Rights, European Union, United States of America, International Law and International Criminal Law to name just a few.To the left you see a very reduced image of such a map, but a few main keywords are still discernible.

These extra large topics veil the keywords just below. Zooming in will eventually bring you to the overshadowed keywords, but at a very deep level, so you will lose an overview of the structure. To the left we have zoomed in on an area clearly dominated by 'Human rights'. Now if I remove 'Human rights' from this cluster, Gephi will recalculate a lot of values, because one predominant element has been removed. After all, all keywords consitute one network. So the map gets a new shape. Especially, if all of the above mentioned subjects are removed and that is exactly what I have done. All the veiled keywords will float to the surface.

Let us now choose another criterion, in stead of the number of times a keyword occurs, to create a map. Gephi gives us a few other options, one of them is betweenness centrality.

Et voilà, after using the option 'rank parameter' in Gephi and choosing for betweenness centrality a new overall map appears, now with new highlighted nodes or keywords. Before zooming in, I will try to explain what betweenness centrality is. In brief, betweenness centrality is an indicator value for a key position. The higher the value the more important the role of the keyword. This value is calculated by counting the shortest paths between two keywords in our network. The keyword which appears the most times as being in between two different keywords, has the highest betweenness centrality value; these keywords are brokers or intermediaries. I used these values to create the map at the left.

After zooming in a little on the section of the map where the overall keyword 'Human Rights' used to be, a new picture arises. We see keywords like Children, Women and Family law, all of course related to Human rights and quite a few of them with a high key position or broker value. In short a new picture of related subjects emerges, indicating what the library of the Peace Palace could provide to its users.

By the way, the relations of keywords with a high betweenness centrality are not restricted to just one general subject. Between this kind of keywords there could be dense relations to other general subjects as well, see the image to the left. Using Gephi maps not only give students and scholars a tool in hand to explore the collections of libraries, it also is a clear reminder of the necessity of using keywords to conduct efficient bibliographic research.

Those of you who would like to have the data file used in Gephi to create all the maps shown, do contact me at a.janson at ppl dot nl.

My other blogs about 'Gephi in libraries':

• Keywords! Maps! Let's dive in.
• Library and user: one interest?
• Subjects by keywords.