Guys i have a little problem, i tried to find some examples on GeoIP based system that expands searches based on nearest neighbor countries. For example the visitor is from UK and tries to find IPs from France, Spain, Belgium etc. not for example Brazil, Argentina, China. So how can i get nearest countries from a given country/IP and expand incrementing the distance?
Edit: I'm using the free Max-mind version, since i don't care about cities that much. And my project is C# based.
Well, the first step to reduce the problem is to use basic geography, and categorize the countries by continents.
From there you can make a list of distances of within a given continent, and sort based on those "distances" or "weights".
The geographic distance (e.g. km or miles) between capital cities should be a "good enough" approximation to get started if you want to be fancy. I bet you could even find such a list with a bit of searching on the Internet.
From there you have the "post-office problem" (Knuth) or "nearest neighbor search" optimization problem, and in this case I suspect you can [REWORDED] simply go with a linear search within the continents partitions. If you need better performance, then an approximate algorithm approach should suffice. (answers are not guaranteed to be best solution, but should be reasonable most of the time)
Note this form of geography based "routing" is weak in a few exceptional cases, such as Cuba, which does not get Internet access from its (naive) obvious geographic neighbor, USA, and some "black-hole" type countries due to political relations. North Korea and Tibet I suspect are similar cases.