Holidays coming soon
It utilizes pictures posted on Panoramio. An interesting way to use collaborative databases on the internet. Too bad, the seemingly good quality at this scale of the map does not actually enable to zoom in to cities scale. Other maps created for cities can be found here on flikr.
If on the first map only basically pictures density seems to be used, city maps take advantage of more information. For how long the user publishes pictures in a given city, and whether or not he published pictures in others allows to define tourist (red) and local (blue) photographers.