How to compare node location with a geographic region?

Hello everybody

I'm quite new to rules and drupal (I'm starting with D7), and I'm having no luck so far with my specific problem, which is:

Before the node is saved, I need to check if the node (I'm using Location module + Gmaps for the geographic information) is located within a delimited region on the map (it's not a cyrcle, I need to define a polygon). All nodes that are not inside this polygon should not be created (or deleted after creation). Actually this polygon is a geographic real area, so I imagine it could be feasible also checking the city name against some good database of city names, but I'd rather not to use this solution because in my region there are 2 official languages (names are different depending on the language), and I'd like also to be robust against mispelling the names of the cities).

If anybody has experience with a similar need, it would be nice to know at least which modules to investigate in order to go in the right direction.

Thanks a lot

Regards