I came across these maps and was immediately drawn in. I had no idea what the maps were illustrating but their appearance was captivating enough to make me do a little additional research to find out. Photographer and digital cartographer Eric Fischer created maps of 50 cities for which he used the geotags of photos uploaded to Flickr and Picasa to plot out every photograph taken on a street map. He divided the photographers into three camps: 

Blue for locals (people who have taken pictures in a city over a period of a month or more), red for tourists (people who took pictures in a city for less than a month) and yellow for undetermined.