Where to get/extract relational data on administrative regions of the world?

I'm working on a web-application that operates on services. Every service is normally provided over some (possibly several distinct) geographical domain(s) like city, county, region, state, country or worldwide.

Typical tasks:

• users will submit their location as lng,lat and I will need to find what are the services available for them
• when users add new service they should be able to select the smallest geographical domain that covers service area, eg: US->California->SFBayArea.

I wonder what is the best db schema to represent hierarchical relations of geo domains and where to get the actual data for geographical domains?

I started with openstreetmap though it lo开发者_Go百科oks rather complex and it will take considerable time. So I decided to appeal for community wisdom :)

Thank you for sharing your wisdom! Have a nice day!

--UPDATES: updated typical tasks

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For all sorts of geography-related data (though not maps), try http://www.geonames.org/.