Distinguishing "mountains" from "valleys"

[morganherlocker]

It appears that I seem to be not getting back "valleys" in the contourList. What I mean is that I get to polygons repeated at level 1, instead of a 1 ring and a 0 ring for a simple grid like this:

111
101
111

It is a bit difficult to explain in text, but does that make sense?

[morganherlocker]

I am closing this issue. This algo does return the holes at the correct levels, but I was confused when visualizing them as filled bands (with isolines it would be more obvious). I will need to write code for a donut option to get what I am looking for.