Why every map of china is just slightly wrong? First things first, this article is not about the hugely controversial and politically divisive places that you probably assume it is based off the title.
So let’s say you’re you, and you’re on a road trip heading from the bustling city of Shenzhen, China to visit the beautiful Lam Tsuen Park in Hong Kong. You wake in your room at the Sunflower hotel, and head over to the Northeast Dumpling House to start your day with some delicious steamed pork buns—the breakfast of champions.
You drop off a letter at the Fulian Post Agency, make a quick stop at the Bank of China to get a few extra kuai for the taxi, and then you’re on your way to Lam Tsuen park. But wait, what happened to the road? Why is it split in two? Are you in a dream? Did Leonardo Di Caprio hack into your mind? Let’s turn on the satellite map.
Wait, why are you in the middle of the Shenzhen Bay? And come to think of it, why was that bank in the middle of a lake? And why was that dumpling restaurant in the middle of a busy intersection? Why was the post office in the middle of a forest? And why was your hotel in a river? The good news is, you’re not going crazy, and Leonardo Di Caprio is far away, on a yacht with models. Your map is just wrong.
The bad news is that you can’t fix your map, because every map of China is wrong. The 1992 Surveying and Mapping Law of the People’s Republic of China makes any surveying or mapping of mainland China illegal without specific authorization by the Chinese government.
And it’s enforced—from 2006 to 2011 alone, the Chinese government brought 40 cases against people who tried making maps—everyone from Coca-Cola to three British geology students trying to conduct research on fault lines which is definitely one of the lamest ways to get arrested—image being in prison, having Marco the Machete Murderer ask you what you’re in for, and your answer is, “cartography.”
Not exactly hardcore, but, according to the text of the law, the Chinese government believes that keeping its geographic data secret is important for “development of the national economy, the building up of national defense, and progress of the society.”
And they’ve gone to pretty extreme lengths to make sure that nobody knows where anything in China actually is. There are only 14 companies that have been granted permission to make maps of China, and all 14 are Chinese—not a single foreigner has been allowed to map the country.
That means that companies like Google have to partner with Chinese government-approved mapping companies, like AutoNavi, in order to have maps of China at all. But you might be wondering, if all these companies are allowed to make maps of China, then why are all the maps wrong? Well, that’s because the companies make accurate maps, and then they intentionally mess them up.
You see, most countries in the world use a GPS coordinate system called WGS-84. WGS stands for World Geodesic System, and 84 is because the system was established in, you guessed it, 1584….no, it was 1984. But instead of WGS-84, China uses a system called GCJ-02. The GCJ-02 system is like the WGS-84 system but with one major difference.
It takes in all of the accurate GPS coordinates that government-authorized mapmakers have and feeds it through an algorithm that intentionally messes them up—randomly moving coordinates 50-500 meters away from where they actually are. On the one hand, that isn’t a huge difference, but, you know what they say, “close only counts in horseshoes and hand grenades.”
That’s what the judge said after my last knife throwing show, but with the Chinese maps, “close” makes a big difference if you’re trying to drive here, over the Jiaozhou Bridge, and your map takes you here, into the Jiaozhou Bay. But let’s say that you don’t know your way around China and you want to fix your map so that it is accurate.
Well that’s a lot easier said than done because the GCJ system doesn’t shift everything in the same direction or the same distance away. If it just made everything 20 meters further east, you could fix it by just shifting your whole map 20 meters west. Easy, problem solved. But the algorithm is designed so that each individual location is shifted a different random distance in a different random direction, which means that piecing it all back together is a lot more complicated.
The only way to make things look right is to make the entire map, including the satellite map, use the GCJ system, which, for example, is what Google China does. So if you go to google.cn, you’ll notice that the Bank of China is no longer in a lake which is great for the Bank of China’s foot traffic, but doesn’t mean the map is fixed.
You see, the bank isn’t on land now because the satellite map is right. It’s on land because the satellite map is now also wrong. So instead of google.com, which puts an accurate satellite image over an inaccurate map, google.cn puts an inaccurate satellite image over the inaccurate map.
So everything lines up, but it’s all still completely wrong. The coordinates it gives you for a location are just not the real ones of that location. It’s like fixing your wrong answer on your geography test by crossing out part of your textbook and writing in that actually, the capital of Florida is Florida City.
So if on Google China, you go to a border between mainland China and an area that uses a correct GPS system, the images don’t match up. If we go to that same bridge from earlier on Google.cn, on the border between mainland China and Hong Kong, the bridge is split in two. That’s because it’s trying to match up the accurate satellite images of Hong Kong with the inaccurate satellite images of mainland China.
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