You can see how much Google skews their map for China, such as by looking at Beijing:
http://labs.strava.com/heatmap/#15/116.46747/39.94133/gray/b...
Vs a similar map for Tokyo: http://labs.strava.com/heatmap/#15/-220.36217/35.60747/gray/...
Vs a similar map for Tokyo: http://labs.strava.com/heatmap/#15/-220.36217/35.60747/gray/...
Bike maps are likely created directly from GPS paths, which are unskewed. When you look at Bejing, you can easily see that difference.
E.g. http://academics.wellesley.edu/Chemistry/Chem105manual/Appen...
The Chinese Street maps are very precise but consitently inaccurate (the skew). The GPS tracks shown are relatively precise and accurate.
The change to the GPS signals (by not encrypting as much of the timestamp data) improved precision.
https://productforums.google.com/forum/#!msg/maps/ambcCIPTQi... says that the satellite images are correct and that the street maps are misaligned.
They claim that the offset is for security purposes but this simple fix shows that the excuse is bullshit. In reality the Chinese put all kinds of barriers to entry for foreign companies to make it difficult to penetrate the market. Another example is that you have to dual home your servers to both china unicom and china Telecom, as the traffic between the two networks is degraded on purpose. You thus have to purchase a special DNS service that differentiates between requests on the two networks.
In the same vein, the purpose of the great firewall is more economic than political, being a highly successful form of protectionism.
It seems a tiny amount of work compared to, say, gathering the actual street data itself; and it would be an useful thing to make this data available to the public like openstreetmap data.
1. The data is reported from a many varieties of GPS devices and phones. So the data is noisy. Some singles tracks will be very noisy, to the point of being fiction.
2. Not all of these tracks are on the road. If you click between bike/run/both you'll see the bike rides are more correlated with roads and the runs seem to have more "off roading."
3. some of those paths are sidewalks and pedestrian bridges and underpasses.
The major routes are offset north and west of the actual roads: i.e. People are not really running/riding through lakes and rivers ;)