Why GPS makes distances bigger than they are

From the abstract :

Global navigation satellite systems such as the Global Positioning System (GPS) is one of the most important sensors for movement analysis. GPS is widely used to record the trajectories of vehicles, animals and human beings. However, all GPS movement data are affected by both measurement and interpolation errors. In this article we show that measurement error causes a systematic bias in distances recorded with a GPS; the distance between two points recorded with a GPS is – on average – bigger than the true distance between these points.

Brian Hayes did some experiments with running on a track and connected them to this paper: http://bit-player.org/2015/the-long-run