Four common neighbourhood types: which one to use?

Discussion created by tayler.hamilton on Mar 25, 2011
I use focal statistics quite often and I can't seem to find the answer to the question:

Which neighbourhood type (rectangle, circle, annulus and wedge) should I use and why?

I am looking at statistics of landcover types and have been told that the circle is the best type to use because it yields the smoothest looking results.

Can anyone else offer a better explanation? I have been looking in the literature and still can't seem to find an answer.

Thank you