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.

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

What are some techniques to accomplish this?

Answer 1

I've answered to that kind of question there: https://stackoverflow.com/questions/4373730/is-there-an-offline-geocoding-framework-library-or-database-for-ios/4419113#4419113

The compilation of spatialite under iOS is not that easy. I struggled for a while before having something that works OK.

I have made a pdf file that explains the steps required to compile spatialite (+GEOS and PROJ4 that are required to get spatial indexes working properly with spatialite), I made the compilation of the whole stuff under XCode.

If you're interested in such PDF, just tell me, I can send it to you.

Answer 2

I would look into using Spatialite. It's sqlite + spatial functions and indexes. It'll do what you need and should(?) work on iOS.

See also: Reverse Geocoding Without Web Access

Answer 3

In addition to spatialite you could also use a raster approach. Simply convert the vector to a sensible resolution, and include a lookup table for attributes in your code. It will not be terribly accurate close to boundaries but should be very fast if you get the correct formats and compression.

Answer 4

Most solutions answered here need some libs for spatial functions (R-Tree and etc). There is a simple solution that does not need libs at all to do reverse geocoding. I have answered this in another question (https://stackoverflow.com/a/73027520/17219971).

The solution is based on run-length-encoding and is very simple to use. You could put the data into a regular SQLite DB and the query is efficient. See the linked answer to learn how this works.