Un GPS finalement pas très précis : un exemple avec ShopKick

With your location increasingly being utilized in mobile apps, an important question is just how accurate is your phone’s GPS? According to data obtained from shopping rewards app Shopkick, not very.
Shopkick, which uses a device that makes an inaudible (to human ears) sound to automatically and precisely check people in when they enter stores like Best Buy and Target, has also been keeping track of where user’s phones say they are when they enter Shopkick-enabled locations.
The results are plotted on two maps — one of New York and the other of San Francisco — with the green markers indicating the Shopkick location and the blue markers indicating where GPS plots the users at the time of arrival:
As you can see, there are lots of markers clustered around the stores, but also plenty of them at 1,000 feet or more away from the location.
Shopkick, which also just passed one million users, has an obvious incentive in highlighting this problem: its app is about as good as it gets right now in terms of allowing retailers to actually verify a mobile user is at their location, and hence eligible for the incentives and rewards that it offers.
A criticism of Foursquare and its deals is that users can accumulate rewards and mayorships by checking in even when they’re not at a location (though the company has moved to pull GPS data into the equation, at least making sure you’re in the vicinity). Thus, one of Shopkick’s selling points with retailers is that it doesn’t suffer from this problem.
Ultimately, this data should help Shopkick make its case. That said, Foursquare said this morning that it already has 250,000 businesses verified on its platform (and rolled out several new options for them to create promotions), so it seems that for now there’s room for multiple approaches to offering location-based rewards.

Source : http://mashable.com/2011/03/09/smartphone-gps-accuracy/