Parametric surface item list

Hej

I am sitting with a problem i always seems to run into. Its how to get some specific points from an item list, and have does points parametric related to the amount of point, so i get the same points no matter how much i divide the surface in to. 

I have been using all the commands that i am sitting with, cull, item list and so one.

Its the point which have a black circle around on the picture.

Regards