Foursquare is tapping into its data of foot traffic for the first time to predict Apple’s iPhone sales as the new iPhone 6s and 6s Plus launch this weekend. The company notes that it has “the world’s largest database of information on the foot traffic of people around the globe,” courtesy of its app users that use the app to check-in at locations they visit. 

For its prediction, Foursquare compared its foot traffic data for Apple Stores to Apple’s own data for opening-weekend sales on past launches. It realized that the increase in foot traffic data surrounding iPhone launches aligned nicely with the increase in iPhone sales from past launches and used that model to predict this year’s sales. The model predicts that Apple will sell 13-15 million iPhones:

Combining Foursquare’s foot traffic data with Apple’s sales data on a graph shows how closely the two are linked. Visit growth is clearly a strong general advance indicator for sales performance of the launch weekend… Based on these early indicators, Foursquare predicts that launch day foot traffic will be about 360% of a typical Friday. This likely means that Apple will sell 13–15 million iPhones this weekend, surpassing all previous records.

Foursquare does note in its report that its foot traffic data doesn’t directly take into account preorders, which Apple included in the first weekend sales numbers when reporting in years past.

Compare the prediction of 13-15 million iPhones from Foursquare with market expectations of around 12-13 million units, as noted in a report yesterday from KGI analyst Ming-Chi Kuo. In the note issued to clients, Kuo described two likely outcomes for opening-weekend sales. In one scenario, KGI predicted sales of 12-13 million units pleasing investors, while in another prediction it had sales of 10-12 million units triggering a “mixed market response.”

Earlier this month, following preorders going live for the new iPhone 6s and 6s Plus, Apple said it was on pace to beat its opening-weekend sales record of 10 million units.