Let me attempt to put this in the simplest terms I can. Eric Fischer, a photographer and clearly someone who knows his way around a computer, has created beautiful, ghostly maps from pure data. These maps are formed using the location tags (geo tags and ID3 tags) placed on images uploaded to Flickr. What Eric then did was color code them according to whether the photos were taken by tourists or residents of that country. Eric has done this with 50 cities across the globe to visualize the difference between home grown and foreign photogs habits. The potential here is quite remarkable, knowing where tourists take the most photos means knowing where businesses could tap into extra revenue and where newly transplanted citizens should avoid living, among other things.
You can see all the data-fueled maps here.