How to get the surface boundary base line

Hi guys:

How to get a selection of multiple surfaces at the bottom border ?
How to fix this ?

TSF-0229-w2-Q1.dyn (3.0 KB)

you may start by extracting the Z vector from the end & start point for each of the curves. let’s assume the " base " is @ 0.00 … so the curves that have a Vector Z = Zero in both start & end point of the curves are the ones you are looking for. give me a bit of time and i’ll post the solution

@Dornan_Luke Check this out.

if your reference which is the “base level” has changed then all you have to do is change the values in the code block {{0,0}} to match your desired level. & keep an eye on the lacing in the nodes. good luck !