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I am looking for an additional source for geocoding and reverse geocoding. I went to http://www.openstreetmap.org and clicked the button to query my current location. Nominatim returned a "house" with my correct address. When I search for my address, I get the same point. So I figured that someone must have entered a node with building attribute of house and my address. But when I download the OSM data for my state into QGIS, and then create a point layer with it, when I filter the layer on nodes with "building"="house" set, there are only 330 or so in the entire state, all spread out. Like only people who have added their own house have these nodes, perhaps. The majority of nodes that have "addr:streetnumber" set are for businesses, churches, and other POI entries.

Which brings me back to the original question - how does Nominatim know of my house? FYI I also created a layer of the closed polygons, thinking the house may be there, but it is not there, either.

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I posted the question because it took me a while to find the answer, and maybe this will help others.

I learned that Nominatum uses OSM data AND tiger map data as input in the US, because address points are rare in the US, but people still want to geocode to an address. While Nominatum did return a "house" point - this was actually an approximation - it found the street segment that would contain that street number, and interpolated to approximately where the house should be. When I double checked the lat/long returned on a map I have with satellite image, it was actually not at the right house. Close, but not quite.

Unless you are doing work in a town willing to share its master address layer or parcel layer or building layer, exact matches to the driveway will be difficult to get unless you pay for geocoding services from one of the many that provide good matches (Here.com, mapquest, google, bing, etc).

If someone knows of a free or very reasonably priced geocoding service that doesn't have a 14 page usage policy that likely eliminates my application :-) ), I'd love to hear of it!

For smaller towns, I'd almost be willing to pay for someone to drive/walk the streets and tag the driveways for me! Need to find the best app for that on a phone...

  • You can install your own Nominatim instance if the usage policy of OSM's Nominatim instance doesn't fit for you. – scai Sep 19 '16 at 15:17
  • Thanks. If I get a good source for master address points (like a point at the driveway for each valid address) perhaps I will find a way to add that proprietary information to nominatim and simply use it and its API for geocoding. If the master address point is NOT found, nominatim can do the street segment interpolation for me as an approximation. – Brian B Sep 19 '16 at 17:25

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