From The Atlantic:
There is an old story about Sam Walton: In the early days of Walmart, its founder would monitor how stores were doing by counting the cars in the parking lot. After seeing the power of satellite imagery in his factory deal, Tom had a similar idea, but on a scale Walton could not have imagined. He asked his brother, "What if we could count the cars at every Walmart?"
After a week together in the Rockies, the brothers had a plan. Alex left DigitalGlobe and negotiated with the company to sell him three years' worth of archival imagery. Tom downloaded a mouse-click counter, which allowed him to count the cars in those photos by clicking on each one. After a few months of scouring parking lots – at Home Depot, Lowe's, McDonald's, and, yes, Walmart – the brothers had a data set to back-test. Sure enough, the number of cars in a retailer's parking lots seemed to accurately predict the company's revenues.
The Diamond brothers started their own company, called RS Metrics. (RSstands for "remote sensing.") Their first client was a stock analyst who asked them to count cars at McDonald's, now using real-time satellite imagery. Lowe's hired them to keep tabs on its own stores – and on Home Depot's, too. Their big break came in mid-2010, when Neil Currie, then an analyst at the investment bank UBS, bought parking-lot counts for 100 representative Walmart stores and published the results in a quarterly earnings preview. The number of cars in the parking lots, he wrote, suggested that Walmart stock was undervalued.