Two words: Mercator Protection.
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This would make a great addition to āInvisible Citiesā.
When Iām in China, the 500m shift is really annoying. But itās consistent for each session. So you go to a landmark (intersection will do), see where the GPS says you are, and mentally subtract that offset for the rest of the day.
Turns out mapping apps in Chinese donāt seem to have the same offset. But I canāt read Chinese very well. I could at least download Google maps ahead of time, but Google has recently started blocking this for China. I used to do that for towns Iād be in so I could find my way around. No more.
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Itās not quite as random as the article makes out. And, in fact, if your GPS uses maps from a licensed provider, the position will be fine. In the example, if the two friends, just metres apart were using the same app, the odds are that their positions would still be just metres apart, but might appear to be some hundreds of meters from the actual location.
Ironically, in my experience, Apple maps seems to be the most accurate, always getting the location spot on. Iāve also been living and driving in China for almost 7 years, Both cars that Iāve owned in that time (US brands: Buick and Tesla) have had perfectly good GPS.
Ironically, adding random offsets to GPS positions isnāt a Chinese invention. The USA created GPS with built in errors (up to 150m - if I remember correctly) for non-military users, but had to switch it off when commercial concerns invented systems that counteracted the randomisation and improved on the accuracy by an order of magnitude.
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What would Gall-Peters do?
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Except that Mercator projection wasnāt designed for political purposes; it was designed so that a rhumb line (a line of constant bearing) would accurately connect two points. Thatās kind of important when navigating a ship by map, compass, sextant, and chronometer.
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Nice catch!
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The Soviets actually put some nontrivial effort into their deliberately-munged maps. Aside from thatā¦special flavor of motivationā¦that putting the State Survey and Cartography guys directly under the NKVD on the org chart; they had G.A. Ginzburg (apparently one of the top mathematical cartography people they had available) design a specialized projection for producing suitably distorted maps for civilian and other non-classified uses.
(Also, your fatherās co-worker might have gotten off lightly: he was probably lucky that his workplace had a āsecret stuffā safe; and that his boss decided to overlook the fact that he had been wandering around with an illicit high-quality map; and just shove it in the secrecy stash and operate as though it had always been in there.)
The 1948 special
instructions for using and storing topographic
maps required that they āmust be kept in the
way accepted for secret and office-use documents
. . . Persons who, as a result of poor storage or
negligent use, lose or misuse a map qualified as
<> or <> will be
subject to criminal prosecutionā
Unfortunately Giznburgās stature as a mathematical cartographer means that my attempts to hunt down the actual projection he designed for the purpose have been in vain. A variety of projections he designed show up in academic literature, even in languages I understand; but all the ones Iāve been able to find appear to be academic work aimed at making good maps, not state-security work aimed at making carefully bad maps from good data. Iād be a little surprised if the projection is still buried in a classified archive somewhere; but it doesnāt seem to be easy to come by; much as Iād like to.
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Could you source several of the distorted maps, compare them with the accurate ones using landmarks that are common and donāt move, and try to reverse-engineer the algorithm?
i think iāll never find my hotel if i travel in China 
Iāll just leave this here: http://repo.xposed.info/module/com.oasisfeng.google.maps.rectify
I do love xposed 
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However, if China does this obfuscation and their citizens become knowledgeable about the practice, wonāt those citizens 1) use another digital product that gets them correct, un-obfuscated information, or 2) use (ostensibly illegal-to-produce by the unsanctioned) paper copies? And doesnāt this water down their national defense in that the stateās own citizens will likely face more challenges with regard to local or national navigation in times of emergency? And doesnāt this also doom local developers/planners or other people who might want an uncorrupted data set for actual, beneficial use?
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Despite his stature in the field, he doesnāt even rate a wikipedia page that I could locate. I found one of his books (Cartographic Projections, 1951), but thatās it.
I too am trying to track down the references. But I donāt speak Russian, so itās doubly difficult. The sentence at issue reads
In the 1970s even the basic 1:2,500,000 map was deliberately impaired in a very tricky way. Higher authorities of the Main Administration of Geodesy and Cartography of the Council of Ministers of the USSR ordered its Central Research Institute to perform the task. Professor G.A. Ginzburg, the leading specialist in mathematical cartography at the Institute, constructed a special cartographic projection, the application of which led to implementing random distortions in coordinates, distances, and directions on the map. Ginzburg was awarded the State Prize for this achievement.
But itās uncited. Moreover, Ginzburg does not seem to appear in the wikipedias list of State Prize honorees
My curiosity is whetted. It is not yet sated.
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