Create surface from curves


I am new to grasshopper. I am trying to create a surface from all these points. It only let me to create the surface when all the points are on the same level. When all the points are not on the same level, it won’r let me create a surface. I have try “loft”, “surface from points” and “boundary surface”. Hope someone can help me. I will really appreciate your help!

Using boundary surface.
This is what I am trying to make.

Thank you!

Sorry, forget to upload the GH file and Rhino file
chicago-illinois-us.3dm (3.9 MB) (66.2 KB)

You can use Delaunay Mesh

It works! Thank you so much for your help!!!