Foursquare, which has gotten out of the check-in business (well at least they've put it off to the side) and focused more on local recommendations, has a lot of location data at its disposal.
And it recently used said data to make a prediction about this weekend's iPhone 6s mania.
According to Foursquare, Apple will sell between 13 and 15 million new iPhones this weekend. That would be a record for the company.
To make this prediction, Apple looked at historical foot traffic to Apple stores leading up to previous launches, as well as Apple's public sales data.
"For each launch, visits to the Apple stores spike in the week leading to launch day with a major spike on launch day and shortly thereafter. Over the last three years, foot traffic has increased by 200 to 300 percent on launch days over the average Friday," says Foursquare.
"Looking at Apple earning reports from the same period, we can assess how launch weekend sales volumes perform versus normal weeks. In 2012, Apple reported sales of around 5 million units — an increase of around 140% over the normal weekly sales volumes that quarter. In 2013 and 2014, Apple sold around 9 and 10 million units, an increase of around 245% and 230% respectively."
Based on this link, Apple says foot traffic at Apple stores this Friday will push 360% that of a normal Friday.
Of course, a lot more goes into sales that foot traffic and historical sales data. But Foursquare's prediction isn't that much higher than Apple's own shipping figures.