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I've spent close to two full days trying to understand the nature of the infamous GPS shift in China. After sifting through the noise, two recurring symptoms are that:

  1. GPS coordinates (WGS-84) plot poorly on Chinese maps, with an offset ranging from 50 to 1000 meters.
  2. Google and Apple Maps in China have severe misalignment between their street maps and satellite imagery (live example)
    enter image description here

Various sources make contradictory claims:

  • Cold War-era regulations mandated introducing random offsets into GPS chips due to security concerns
  • protectionist measures aimed to favor GPS devices manufactured in China
  • China simply uses a different projection system, and the offsets are not random
  • GPS chips manufactured in China offset the coordinates they return, in order to match approved Chinese maps, which must follow the GCJ-02 datum

What is the actual story? This looks like the type of pervasive problem that merits a Wikipedia page, but I haven't been able to find anything authoritative yet.

The two questions suggested as possible duplicates don't answer exactly what the cause is; rather, they describe symptoms.

  • @Chris: does it not seem likely that this question, as PolyGeo re-titled it, is better phrased than the false-lead one about the urban canyon? – Dan Dascalescu Apr 6 '15 at 7:24
  • I would not disagree. I'd probably say the answer there that best fits here should be moved, since imho the laws/etc. and talking about offset don't address that actual question of getting any signal and technical performance. I just voted it because I knew that answer was there and had been recently discussed. gis.stackexchange.com/questions/59931 (which is referenced in said answer) might be a better candidate for marking as duplicate. Alternatively, leave both open, link them via comment, and put the answer in both places (your wording is definitely better for this issue). – Chris W Apr 6 '15 at 7:47
  • The pages you have linked to about China using a different projection system, have nothing to do with the behavior that you are observing. – Devdatta Tengshe Apr 6 '15 at 11:55
  • @DevdattaTengshe: that demonstrates my confusion with the situation, which is why I've asked to have this clarified. Would you please vote to reopen the question? – Dan Dascalescu Apr 6 '15 at 20:56
  • @DanDascalescu: an you explain why gis.stackexchange.com/a/59936/442 does not clarify your confusion? I'll try to expand that answer to cover those points – Devdatta Tengshe Apr 7 '15 at 4:22
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The problem is poorly documented by authoritative sources for English speakers, despite affecting millions of people on an everyday basis. I've spend the past two days trying to understand the situation and I've created a Wikipedia article about the restrictions on mapping in China and about the China GPS shift problem. Below is the part of my research that answers the question.

The root of the problem is the severe restrictions that the Chinese State Council places on geographic data concerning China's air, land and waters. Mapping and surveying can only be done with authorization from the State Council, and foreigners must form a joint-venture in order to be granted authorization for surveys. There have been numerous examples of fines levied against individuals and companies breaking this (cough protectionist and isolationist cough) law.

Online map providers offering street maps of China must obtain an authorization from the State Council. These maps must use the GCJ-02 datum, instead of the WGS-84 that the most of the world uses. This causes WGS-84 coordinates, such as those coming from a regular GPS chip, to be plotted incorrectly on GCJ-02 maps.

run log is offset

The street maps displayed by both google.com/maps and google.cn/maps use GCJ-02 coordinates. This can be proved by getting the GPS (WGS-84) coordinates of a known landmark, such as the Monument to the People's Heroes in Shanghai, which is located at 31.24427 N, 121.48695 E:

I'm still unclear as to whether GPS chips manufactured in China return GCJ-02 coordinates directly, or if they return WGS-84 coordinates, which approved map software can convert to GCJ-02.

  • I went through the Android source code, and did not find this shift anywhere. This leads me to believe that the GPS themselves give out transformed values; Given that most consumer level electronics are produced in china, it is possible that their firmware produces Results in GCJ-02 – Devdatta Tengshe Apr 10 '15 at 5:28
  • Can you share the GPX with which you drew the red line on the map? – Devdatta Tengshe Apr 10 '15 at 5:29
  • @DevdattaTengshe: unfortunately I don't have the log - I found the plot here. However, we know for sure that maps of China are made using GCJ-02. Pan to Shanghai in an OpenLayers and toggle between OSM, Bing Aerial, and Google Streets. – Dan Dascalescu Apr 10 '15 at 6:55
  • So does Google satellite imagery render as correct? I ask because while using Google maps API, Google terrain and Google road show shifted map compared to satellite map (and to pointed monument coordinates). Which one is correct? – zetah Aug 26 '16 at 10:32
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@ Devdatta Tengshe Google maps app gives out transformed values to match with GCJ-02 maps. Open Google maps webpage on you cellphone, locate, and you will find your cellphone gives you the right WGS-84 coordinates which do not match with GCJ-02 maps. So it has nothing to do with hardware, firmware, or Android, it's the apps who want to cater to their Chinese customers or customers who spend a lot of time in China make the WGS-84 to GCJ-02 coordinate transformation. Check this out: http://www.sinosplice.com/life/archives/2013/07/16/a-more-complete-ios-solution-to-the-china-gps-offset-problem

  • How do you know that you are getting the right coordinates? what will you compare them to? – Devdatta Tengshe Sep 22 '15 at 10:22
  • I have Google Earth which is technically not a map and it always gives right WGS-84 coordinates. – Guest Sep 23 '15 at 8:16
  • @Devdatta Tengshe Obviously I'm in China, and I did check up on it. I typed in the WGS-84 coordinates of a famous building right beside my office, on Google maps webpage I was located right beside it, and both of us were at the wrong places on the GCJ-02 map but right on the WGS-84 satellite image (Google Maps app offers GCJ-02 map and WGS-84 satellite image and they certainly do not match with each other). Big companies like Google paid to get their map apps to transform WGS-84 coordinates to GCJ-02. So called security concerns are ridiculous, this is a business. – Guest Sep 23 '15 at 8:51
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I just came back from Shanghai. Using Google Maps on an iPhone 6+ I experienced an about 500m shift to the northwest of my actual position. Apple Map worked fine.

A friend of mine cross-checked with Google Maps on her Android phone and there the location was correct.

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