The purpose of this map as detailed on Daily Kos is to represent the congressional districts in the United States accurately. Currently it is difficult to show the districts because some such as those in New York City are very small, while others like Montana are the size of an entire state. Previosly the maps needed to be zoomable to see the districts containing cities. Other representations such as cartograms warped the country's shape. This map attempts to fix that by giving each congressional district equal area i.e. five regular hexagons.
The data about Bernie Sanders' events comes from the non-affiliated website bernie2016events. The data that I parsed is a about two weeks old, so it is not completely up