I recently came across a post on FlowingData with a visualization showing the growth of the WalMart chain over the years. It’s very well done, but all those icons really clutter up the map. The fact that they’re semi-transparent makes it possible to distinguish the dense areas from the sparse ones, but it’s difficult to tell those intermediate shades of green apart from one another. It sure would be nice if the color varied across the map instead… heat maps to the rescue!
I’ve put together my own animation of the WalMart dataset using ModestMaps and the HeatMap component. The visualization is most impressive when you’ve zoomed in far enough to see all of the major roadways converging on the large cities. From there you can watch as WalMart takes over the urban areas, turning them red hot while leaving the less populated areas (relatively) cold and blue.
Unfortunately my dataset is somewhat incomplete. The version I grabbed from Thomas Holmes has addresses for each store, but the geocoding service I used failed to convert about 100 of those addresses to latitude and longitude values. If anyone can point me towards the complete dataset, I would love to add those missing stores to the visualization.
Before I close I want to give a nod to Universal Mind. Last week they released SpatialKey, a heavy-duty temporal-spatial visualization tool that really shows off the strengths of heat mapping. They’ve taken a crack at the WalMart data set as well, and it’s impressive to say the least. Congratulations on your launch, UM.
Icons by famfamfam.com