I found a couple of fascinating examples of the use of data repositories over the Web. Both deal with Walmart’s spread all over he US, since its opening.
The first example uses freebase as the data provider. Freebase is a “social database of things you know and love” which collects data-provided by users- on all imaginable topics. So, New Zealander “author, software developer and data magnate” Toby (now living in San Francisco) queried Freebase about all Walmart stores in the US, along with their location (ZIP code) and opening date. He then got data to relate each ZIP code to latitude and longitude coordinates, which could be posted on a map. Last, he only had to place dots on a US map according to the date he collected through Freebase, and voilá, he got this amazing animation.
On the other hand, after seeing this, Nathan Yau, UCLA student working out of Buffalo and thinker in FlowingData (a spectacular site showing off data visualizations), did more or less the same thing with another set of tools, the Open Source library ModestMaps. His animation is here.