Which map in China to use

[jbroadhead]

China shifts imagery and street maps 50-500 meters apart. Should map my observations to the correct imagery location or the street location?

[twainwright]

See this related topic: https://forum.inaturalist.org/t/roads-displaced-from-satellite-imagery-on-google-maps/46816
Not sure it answers your question, though. Do you use any kind of GPS for locating your observations, or just postiion them on the map by hand?

[jdmore]

@twainwright

Do you use any kind of GPS for locating your observations

I would guess that GPS signals are also degraded there.

[nrg800]

China is different to the examples brought up in that linked thread (where the issues is an error in the satellite imagery offset), in China, however, relevant laws require mapping companies to offset their public geospatial data by a random (but algorithmically determined) direction and amount. So if you’re seeing the roads offset from the satellite imagery, this means you’re seeing the ‘true’ position of the imagery and the roads offset to the GCJ-02 standard. So you should use the satellite imagery as the basis for the pins you put the observations down with.

I believe if youre accessing the imagery within China, google offsets BOTH the satellite imagery and the road data, which means it visually matches up but doesn’t show the true coordinates, if this is the case and you want to observations to be more accurate then you need to convert the GCJ-02 coordinates to WGS84 Lat, Longs. This can be done (including in bulk) using this tool, assuming it isn’t blocked in China.

But yeah, over China if you’re seeing a mismatch between the satellite imagery and the maps data, use the satellite imagery.

[pisum]

@jdmore

I would guess that GPS signals are also degraded there.

are they? i’ve heard stories of chip and consumer electronics makers implementing blocks on geotagging when they detect a location in China, but as far as i know, the signal from GPS satellites is the same when received in China vs anywhere else.

so if someone were to place observations based on the coordinates determined by a GPS device, those should be as accurate in China as anywhere else. the main problem is that folks doing this might run afoul of Chinese laws related to surveying and mapping without authorization.

[SQFP]

Second that, my obs taken in China with the help of a GNSS receiver appear at the correct location on iNat’s Google satellite imagery (as accessed from outside China). The road vector overlay is completely off though.