During the last few months, I have done some start-up experiments trying to map my home area of southern Sunnmøre, Norway. However, I have noticed that in many places there is a mismatch between the pre-drawn coastline and the GPS traces. The mismatch seems to be quite consistent, approx. 50 meters too far north, and also a little too far west. However the coastline matches quite well the aerial maps (both Yahoo and Open Aerial), so I wonder if there is some systematic error in the software that produces this inaccuracy? Until I have more GPS tracks I can't rule out an error in the GPS tracks, so for now I will not edit the coastline. However this leaves the road 50 meters into the ocean many places, not quite desirable, so if someone has the capacity to make more tracks and verify the error, it would probably be a goood idea...