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I'm looking at the coordinate differences between Google Maps and OSM. I'm a noob in the technicality behind GIS.

Having read:

  1. EPSG 3857 or 4326 for GoogleMaps, OpenStreetMap and Leaflet

  2. How to adjust the difference between the coordinate from OpenStreetMap and Google Maps

I'm not sure whether is it because of #1 or #2 that causes the difference for the same coordinate that appear few hundred meters on the projected map.

And the differences between the data stored and the projected map when using lat/long.

Thanks!

EDIT

This may be more specific to China and the infamous offset issue.

Looking at the following coordinates: 31.230548,121.470965 for the Shanghai Art Museum on Google Maps and ditu.

Having entered the same set of coordinate in OSM, it gives me the Shanghai Art Museum is about 400M away in the NW direction.

I don't understand why a physical point in space is different on the projected maps? Is this specific to China?

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Please post a screenshot and/or code of what causes your confusion. Currently it is not clear what kind of answer/insight would help you. –  underdark May 5 '13 at 16:29
    
As Underdark has mentioned, we can't answer your question, unless we see what exact problem you are experiencing. Generally speaking there should not be a difference between the two service, but often there is, due to the origin of the datasets. –  Devdatta Tengshe May 5 '13 at 16:33
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Updated my original question to include a specific example. –  Nora Olsen May 5 '13 at 16:45
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1 Answer

If you look at the various data sources , you will see that OSM matches very well with Google's Satellite View. You can check it with this excellent tool from GeoFabrik. Just mouse over various locations, and you will also see the mouse location on the other map.

http://tools.geofabrik.de/mc/?mt0=mapnik&mt1=googlehybrid&lon=121.463&lat=31.2268&zoom=16

But when you check Google Maps, and the Google Satellite View, you will see that they do not match.

http://tools.geofabrik.de/mc/?mt0=googlemap&mt1=googlesat&lon=121.46834&lat=31.23227&zoom=16

So it is Google Maps, that on purpose are showing incorrect maps.

As to why this is happening, only Google can give you the authentic answer, but my experience says that this must be to meet the statutory requirements of Chinese laws.

A brief reading of The Google forums shows that this issue is well known. For eaxmple see these posts:

More reading indicates that this is done because of the laws of China. See these Blog Posts.

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Does this only happen within China? Because I did some checks on other coordinates around the world and it did match between OSM and Google. The coordinate should reflect what is in the physical space? –  Nora Olsen May 5 '13 at 17:15
    
It's very difficult to answer that. All I can say is that i've never seen this issue out of china. As your second point: there is often a difference between what should be and what is. –  Devdatta Tengshe May 5 '13 at 18:04
    
Openstreetmap should aling with bing imagery, because they have allowed to digitze there imagery for Openstreetmap purpose, while Google did not. It may nethertheless be that both services have bought the same satellite pictures. –  Andre Joost May 5 '13 at 18:16
    
@AndreJoost: The issue IMHO is that Google Maps does not match even Google Satellite View; That is why it does not match with anything else. All other sources (OSM, Google Satellite View, Bing) match with each other. –  Devdatta Tengshe May 6 '13 at 3:46
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