Making 3D Images 2D

I am trying to create a 2D geometric shape from a 3D vector set. I know that what I need to do is simply display only the points that have a Z - axis value of zero, and what will appear is an outline of the image. Then, if I display points, say, from within z = 0 to z = 5, that outline will be thicker. Is there any way that I can do all this?