It looks like GeoPlanet is dead (Is GeoPlanet dead?).
Is there a suitable alternative that covers Parents (preferably Ancestors) and Neighbours? If there's a name for this type of data, that'd be helpful.
Spatial data would be a plus, but I can get by without it for now.
This project may come to nothing, but in case I am ever able to charge for the service I need to make sure I don't shoot myself in the foot with a restrictive licence.