Terrain Approximating Flat zones

[arten]

I think it similar to this… but I believe I have to find a way group my points relative to angles as angles taken from surfaces are not exact .
I think it is more like

1. sorting points
2. grouping them with angle ranges. For example all points which fall between 0-10 degrees one branch
   10-20 second and so on
3. Sort list of my split surfaces using these groups and BANG !!!

How to sort list of surfaces by number of vertices?

Here’s how my code works with your “data”: [sort_vertices_2018Jan31c] sort_vertices_2018Jan31c.gh (24.7 KB) @Michael_Pryor’s version is simpler because, using Dispatch, it handles only two different polygon shapes, as per your model, whereas mine was happy sorting/sifting a wide range of shapes with “3 to 10” vertices into branches of the “data tree” (final results).