The labels on the map are generated mostly automatically. When zoomed out, arXiv categories are displayed, and the position of the category label is computed as the average of all papers in that category. As you zoom in, these category labels disappear, and are replaced by individual labels on top of each paper, so long as that paper is “big enough” on screen. The labels for each paper are determined by analysing the title and abstract, looking for common keywords.
We have now added a third layer to this labelling process: we identify by eye regions of the map that have a definite theme, and give these regions a generic, but not too generic, label. For example, we can identify cleary the “neutrino” area in the north, and the “inflation” area at the interface of hep-th and astro-ph.
These new labels make the transition from arXiv category to keyword labels a bit easier to follow, and also allows you to more easily understand where you are on the map.
In the future we plan to implement a more sophisticated way of labelling that transits smoothly between zoom level, much like in a map of the geographic world. If you have any suggestions for this, please leave us a comment.