The image above was created by Bluemoon, a designers group in Estonia, based on analysis of photos of Panoramio, which takes into account how many photos and their authors are in the area, converting the data in to colours: yellow is high, red medium, blue low, and grey for areas without available photographs [Bluemoon, 2010].
Panoramio is a site where "members determine the content" and the photos focus on geographical locations, which can also reflect a level of social trends by relating distribution of photographs. Each photo, some under copyleft and Creative Commons license, is also a candidate for transfer to the Google Earth Panoramio layer and selected images are transferred every month [Panoramio, 2010a & 2010b].
Panoramio API - Display photos from Panoramio on your own website. [Online]
Bluemoon  World Touristiness Map. [Online]
Panoramio [2010a] Copyright Status of Posted Photos. [Online]
Panoramio [2010b] Welcome to the Panoramio Community. [Online]