Using geotagging to determine what tourists photograph vs what the locals photograph.
Blue points on the map are pictures taken by locals (people who have taken pictures in this city dated over a range of a month or more).
Red points are pictures taken by tourists (people who seem to be a local of a different city and who took pictures in this city for less than a month).
Yellow points are pictures where it can’t be determined whether or not the photographer was a tourist (because they haven’t taken pictures anywhere for over a month). They are probably tourists but might just not post many pictures at all.