Complex geographic analysis

Discussion created by andrea.matranga on Oct 4, 2013
I have a a bunch of polygons representing different ecological niches (combinations of soil and climate type).
For each point p in the map , I want to know how much of each niche X is within 2000km (call this  value  a(X,p) )   and whether the niche is present or not within 100 (call this b(X,p)) .
I would like to create a raster where each point's value is equal to

SUM OVER ALL X of  ( a(X,p)*b(X,p) )  

the idea is: if a plant is able to live in point p, how likely is it to be able to colonize other ecosystems further away?

Keep in mind that I have about 700 ecosystems so I can't do this by hand.

Thanks a lot!