Hello and welcome tot he discussion!
So a little more information would be helpful -
You can create a toposurface in revit a few ways.
If you have an autoCAD dwg that has all of the x,y,z coordinate that can be used to make a toposurface.
If you have a point file from a surveyor - that can be used to create a toposurface.
Or - you can create it by placing points at a specific elevation.
As for downloading a map - I do not know of that feature.
I hope this helps!