when I say a dense plane, I just mean a 3d plane tool with alot of polygons… turn it into a Polymesh3d and then hit divide a few times… dense just means alot of polygons which makes for smooth deformations and a lot of detail
with an alpha, you can draw out the layout you are looking for from a straight, top-down overhead view… draw it by hand or in photoshop or take it directly from a photo… it doesnt matter… then that alpha can be applied directly to that plane to deform it and recreate that layout in 3d… white areas in the image will be raise, and black areas will stay where they are
and if you want to make close-up scenes from perhaps a ground perspective, then that will be a completely different approach… everything you want to see in the scene, you will have to create… just drawing an alpha and then displacing will not work from such a perspective… if you want to see trees and buildings, you will have to actually make trees and buildings and place them in your scene according to your vision
I hope that helps… I dont know what else to tell you without knowing what you’re trying to do in alot more detail