Map Offsets
From Geospike DocWiki
GPS is a global system and accurate the world over. The satellite imagery generally lines up, but the maps don't always. Especially it seems, in China. 'Map Offsets' are a feature in GPS Log that attempts to correct for known Map Offsets around the world.
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The Problem
Some regions have a map that doesn't line up with the satellite (and GPS coords) causing rather bad navigation problems if you rely on the inaccurate map.
You can check to see if your region has an offset issue easily. Open the standard 'Maps' app. Find a landmark like a big road intersection or a river. Then flick between the Map and Satellite views. Do this rapidly and if the areas don't line up, then your map is offset! Try doing the same in GPS Log. If it lines up in GPS Log, but not in 'Maps', then GPS Log is attempting to correct the offset for your current city.
Default view in the Maps app and other Apps:
These images were taken by changing the view from 'Satellite' to Maps', without moving the map. Notice that they do not line up. As your GPS-determined location is correct only on the Satellite view, this can cause some rather bad navigation problems in Shanghai!
The Solution: GPS Log
Enter GPS Log. GPS Log corrects this issue for particular regions by applying offset values. Basically GPS Log has a big list of these values which it checks to see if any should be applied.
However, not all areas are in the list. So if you are planning to travel to a new city in a country where the Maps are known to be inaccurate, check in the forums first that the city has been checked. Updates to the Map Offsets list are included in GPS Log releases, and you can also update them yourself from GPS Log -> Settings -> Advanced Settings -> under 'Map Offsets' -> Update Map Offset Data.
This feature should not affect any countries which don't have this problem, as each offset point has a small area of effect. However, you can turn it off completely if you are worried in GPS Log -> Settings -> Advanced Settings -> Map Offsets.
View in GPS Log:
These images were taken in GPS Log by changing the view from 'Satellite' to Maps', without moving the map. Notice how they line up now. Your GPS-determined location is now correct in both views, the Map is again usable for navigation.
Possible Fix for the China Map Offset
Apparently it's possible to fix the map offset issue in China for the maps App by following the here.
