China datums
Datums in China
Please see e.g., http://www.asprs.org/a/resources/grids/05-2000-china.pdf . On this page we aim to just supplement the more widely known information.
Coordinate systems used in China
Paper maps
Web maps
觀測中國電子地圖諸網站常見座標系統， An observation of Chinese web mapping sites shows various non longitude / latitude systems in use.
Very many of them are plain Mercator projections. They are visible in the URLs generated when "sharing" map views with friends.
Also a factor is the state mandated distortion... 另需考慮政府所規定之偏移…
搜狗 Sogou
- Sogou API (type=1)
Experimentation proves they are merely using the Clarke 1866 ellipsoid, a=6378206.4 rf=294.978698213898 .
$ proj +proj=merc +ellps=clrk66
- WGS84 longitude / latitude
Examples
Here we give examples of how a single longitude latitude pair is located differently depending on which web mapping site one uses!
- http://maps.google.com/maps?q=loc:40,116.5&t=k
- http://ditu.google.com/maps?q=loc:40,116.5&t=k
- http://api.map.baidu.com/staticimage?markers=116.5,40&zoom=14
Note not all sites are actually reachable from inside China, as one can test,