Techniques for offline reverse geocoding on a mobile device?

Question

I am working on a mobile mapping application (currently iOS, eventually Android) - and I am struggling with how to best support reverse geocoding from lat/long to Country/State without using an online service.

Apple's reverse geocoding API depends on Google as the backend, and works great while connected. I could achieve similar functionality using the Open Street Maps project too, or any number of other web services.

What I really want however is to create a C library that I can call even when offline from within my application, passing in the GPS coordinates, and having it return the country and/or state at those coordinates. I do not need finer granularity than state-level, so the dataset is not huge.

I've seen examples of how to do this on a server, but never anything appropriate for a mobile device.

I've heard Spatialite might be a solution, but I am not sure how to get it working on iOS, and I wonder if it may be overkill for the problem.

What are some recommended techniques to accomplish this?

Answer 1

Radven

You will need to get the Shapefiles (lat/lng outline) of all the administrative entities (US states, countries, etc). There are a lot of public domain sources for these. For example, the NOAA has shapefiles for US states and territories you can download:

http://www.nws.noaa.gov/geodata/catalog/national/html/us_state.htm

Once you got the shapefiles, you can use a shapefile reader to test if a lat/lng is within a shape. There are open source readers in C, just google. I seen stuff at sourceforge for shapefiles, but have not used these myself.

The Team at OpenGeoCode.Org

Answer 2

If you're looking for an approach based on a quadtree, try Yggdrasil. It generates a quadtree based on country polygon data. A Ruby example script can be found here.

Answer 3

I can suggest good written offline geocoding 3rd party library. https://github.com/Alterplay/APOfflineReverseGeocoding