The maps are ordered by the number of pictures taken in the central cluster of each one. This is a little unfair to aggressively polycentric cities like Tokyo and Los Angeles, which probably get lower placement than they really deserve because there are gaps where no one took any pictures. The central cluster of each map is not necessarily in the center of each image, because the image bounds are chosen to include as many geotagged locations as possible near the central cluster. All the maps are to the same scale (a square measuring 15 miles on each side), chosen to be just large enough for the central New York cluster to fit. The photo locations come from the public Flickr and Picasa search APIs.
Locals and Tourists tries to map which of these pictures are taken by locals and which by tourists.
Source: Eric Fisher’s Flickr page