baidu-simcity

I spend a lot of time looking at maps. I’ve been called “the human map.” Cartography is one of my interests. Photography is another.

I use Runkeeper when I’m taking photos with my digital SLR, and later match up the GPS tracks to the photos in Lightroom. But every now and then there’s a photo that just doesn’t match up and you’ve got to manually assign it a location. Normally not a problem.

I noticed in August last year that my GPS tracks, when overlaid on Google Maps in Adobe Lightroom, would point to the wrong place on the map. I toggled to the satellite view, and the photo looked like it is in the right place. But you switch back to the map view and its in the wrong place again. What gives?  Notice in the example below, from Chengdu, China, that the park has moved but the “A” location icon stays in the same place. From my GPS data, I could tell that the satellite maps were spot-on, but the road maps weren’t even close.

map-sidebyside

A quick check of Baidu Maps and Soso Maps (two Chinese companies) revealed that everything was lined up perfectly. Microsoft’s Bing Maps, on the other hand, were so far off as to be completely unusable. I started checking other parts of the world — North Korea, Afghanistan, Russia — and they all lined up without this issue. You can even take a look at Hong Kong, where everything lines up, then move just 100 yards over the border to Shenzhen, China, and things are offset again.

Some investigation reveals that the cartography (the map on the left) has been shifted by a random amount (about 0.025°E,0.025°S in Chengdu, but 0.06°E in Beijing) due to Cold War era Chinese regulations.

The net is that the map offsets are not a bug, but rather intentional. There is a secret fixed website at ditu.google.cn. Okay, not secret, but how you would normally find it, I have no idea (thanks MDW for the link).

This isn’t the first time Google has altered its maps to meet Chinese regulations. Both Apple and Google duplicated the Diaoyu/Senkaku islands so that, from a cartography point of view, both China and Japan could own them. Clever.

Not all is lost, however. There are some very clever map enhancements out there. Google had their 8-bit maps. My personal favorite is the SimCity-style maps from Baidu (the map image at the beginning of this post). Very cool.

XKCD always has a special place in my heart, and this comic hit home. Yes, I probably have spent more time looking at Google Maps in the last 10 years, than playing video games.



  1. Erik Nilsson (Reply) on Tuesday 19, 2013

    Interesting article, thanks. Do you know which is more accurate in Google Maps, the satellite view or the map view?

    //Erik

    • Klamek (Reply) on Tuesday 19, 2013

      Like stands in article and from my experience satellite view is only accurate in China (People’s Republic of). Maps are offset roughly 500 meters SE direction.
      That makes really mess on Panoramio where people pin pictures to Google Earth according to map location which is wrong.
      All my recorded GPS tracks in China are perfectly fit satellite view.

  2. Mark Kampe (Reply) on Tuesday 19, 2013

    I just compared a few GPS fixes in Shenzhen and Beijing and found the satellite imagery to be dead on. The problem is with the GPS coordinates of street maps. But at least I know know that they are wrong and I will start using intersections rather than GPS coordinates.

  3. Will Newcomb (Reply) on Tuesday 19, 2013

    Having just moved to Changsha, China, I’ve discovered the offset problem with Google Maps. Interestingly the problem doesn’t exist with iOS maps! However lots of other map related apps use Google map data so they’re useless too. Baidu and other local maps don’t have the problem.

  4. Kristen (Reply) on Tuesday 19, 2013

    AH Thank you for the explanation, we just got home from a trip to China and I was looking at a map view of Macau and a bunch of roads on mainland China side ending in the river….turned on the Satellite view to see everything within Macau matches perfectly and China is a hot mess.

    I brought it up to my GIS guy and he said, oh it’s just a simple transform problem, but figuring Google would be able to fix something like that if they wanted, I assumed there was something a bit more interesting going on.

    Thanks!

  5. Dan (Reply) on Tuesday 19, 2013

    On maps.google.cn, the satellite images and the street maps in China match perfectly. However, the satellite images are the ones that have been shifted to match the “wrong” street maps, and not vice versa. Hence, the GPS coordinates are still wrong on maps.google.cn, but at the least, the maps matches the satellite image…