Today, I learnt a new concept in positioning system while attending a thesis defence at EPFL: MAP MATCHING. Here is a definition coming from the paper "A Method Of Map Matching For Personal Positioning Systems" (Kay Kitazawa, Yusuke Konishi, Ryosuke Shibasaki):

To track human's movements with high accuracy in certain areas, where GPS system is not available, complimentary positioning methods are needed. Personal positioning system using a sensor of acceleration and a gyrocompass together with GPS is now being developed as one of promising methods. Accumulation of positioning errors, however, cannot be avoided. One of the solutions to reduce or modify these errors is "Map matching" technique, which modifies estimated user's position assuming that users are always along road networks.