Download a dataset (that can be read with Gephi, for example a .graphml
file) and open it with Gephi.
Except with geographical data, the position of nodes is rarely given. In order to have a global view of the network structure, several layouts have been designed for graph visualization. The most efficients are probably the force directed layouts. The default Gephi layout is the force atlas 2 layout. In this layout, nodes are seen as negative particles repealing each other, while edges keep them attached. A general "gravity" force attracts them in the center of the image.
Alternative layouts are:
Inside the Gephi interface, on the bottom left part, we can choose the visualization layout. Choose Force Atlas 2
and click on Run
. After a few seconds click on Stop
to stop the computation.
You can try to change the various layout parameters to see their effect.
Useful information (about individual nodes) can be encoded in the figure using different means. It can be some text, a color scheme, or the size of nodes.
We can modify the node sizes according to their degree using the top left window Appearance
.
Choose the nodes
tab and the size icon. Then the Ranking
tab and finally the Degree
and click Apply
.
Let us add some colors to the graph. On the right side, choose Statistics
and then run the Modularity
.
After the computation, go back to the Appearance
and choose nodes
and the color icon. Choose Partition
, you can see a new node property was added by Gephi, the Modularity
. Select it and click Apply
. The modularity is a way to perform a community detection. Here it uses the Louvain method.
On the bottom you can display information belonging to nodes such as Id
or name
. Click on the T
symbol on the bottom middle bar to display the labels. You may drag horizontally the white circles to change the size of the text or of the edges thickness. Click on the small icon on the right of the bottom middle bar to get more options. Click on Configure...
to choose the property you want to display.
Gephi provides several tools to compute useful graph properties. They can give us a better understanding of the network struture and properties.
On the right, choose the Statistics
tab. Let us try to compute the following quantities:
As in the case of a signal, you use filters to remove some part of the data, where there is no relevant information or some information that you are not interested in. This gives you a better view of the remaining information, the one you are interested in, and you can focus on it.
Let us display only a selected number of nodes with the tab Filters
.
Let us try the subfield topology
and:
the subfield Partition
and:
the subfield Range
and:
You can also select a subgraph, copy it and paste it in another workspace.