[Restrictions on geographic data in China](https://en.wikipedia.org/wiki/Restrictions_on_geographic_data_in_China) forces all approved Chinese map providers to run a obfuscation algorithm on the WGS-84 coordinates in all parts of Chinese maps. This method, known as GCJ-02, is generally known as a "public secret" with deobfuscation methods available. However, Wikipedians often tend to record such coordinates without prior deobfuscation, leading to the equivalent of the "China GPS shift (or offset) problem" polluting Wikidata and Wikipedia itself. (Baidu has a further twist on GCJ-02 known as BD-09. Also a public secret.)
This problem can affect Wikipedia, GeoHack, and Wikidata in various means. When importing the data Wikipedians may obtain such data from commercial maps and save without checking; when reading the data in geohack, Wikipedians will find Google and Baidu map links "wrong" due to the shift. Therefore, these things should be done for all Chinese (mainland china minus South China Sea where everyone is using satellite imagery) coordinates recorded:
* [ ] Tag all older Chinese coordinates as "check required". Provide a tool for reviewing them along with deobfuscated values on satellite imagery.
* [ ] Remind users to check new Chinese coordinates for deviation. Perhaps just add a "check required" tag.
* [ ] In GeoHack, provide format strings for these scrambled coordinates. Probably just `{lat,lon}degdec_cn{gcj,bd}`.
Thanks to @Liuxinyu970226 for bringing this up in T127950#3123960. Previous discussions: [on enwp](https://en.wikipedia.org/wiki/User_talk:Dispenser#Providing_.22.28Chinese.29_mars_coordinates.22_interface_for_Coordinates-related_components.3F), [on zhwp](https://zh.wikipedia.org/wiki/%E6%A8%A1%E5%9D%97%E8%AE%A8%E8%AE%BA:Coordinates#.E6.8F.90.E8.AE.AE.E5.AE.9E.E7.8E.B0.E4.B8.80.E4.B8.AA.E8.83.BD.E5.A4.9F.E8.BD.AC.E6.8D.A2_GCJ-02_.E6.88.96_BD-09_.E8.BE.93.E5.85.A5.E5.88.B0_WGS-84_.E6.95.B0.E6.8D.AE.E7.9A.84_coord_.E6.A8.A1.E6.9D.BF).