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I want to locate shops with open street map. For that I send a query to nominatim, a webservice which geocodes coordinates from addresses. I draw a marker at the returned coordinates, and it´s inaccurate about 100 m. (~300 ft). To double check, I search the coordinates on google maps, and it is also the same (wrong) position, so the error seems to be at nominatim.

Now I type the address I gave to nominatim and search with osm and google maps, where as osm returns the same inaccurate position, google maps returns the correct.

Is it possible that OSM and Nominatim back on the same data in the background (like TIGER?). I'm located in a small town in Germany, is it possible that these areas are still too inaccurate?

Can somebody tell me whats wrong there, or if I can solve this?

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1 Answer 1

Daniel,

It may be that some points in OpenStreetMap are incorrect due to human error, but it's very unlikely that a lot of them are, unless:

  1. There is some projection error in Nomantim or something or
  2. All the points are in the same area, and have been traced from an aerial photo which was poorly georeferened

If it's 2 then there's not much you can do short of resurveying yourself (the beauty of open data), although Germany is the best mapped country in OSM, so I find this unlikely.

Which Nomantim are you using? I get good results using http://open.mapquestapi.com/nominatim/. Can you give us an example of some locations that you believe are incorrect, and we might be able to be of more help?

Have you looked at http://www.openstreetmap.org to see if the locations appear on the map as you would expect?

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