Wow, great design and detail there, and surprised by the finish from pine. I will try some maple and see how I get on. It's the tear out I'm trying to reduce as it's taking so long to finish. I'm using a 5mm downcut spiral flat bit.
For David, your process will depend on what data you can get. You ca trace (digitise) paper maps in inkscape as a one-off, but there is plenty of free DEM (digital elevation model) data out there, especially for the US. I'm in the UK and there's far less available for free.
My method for layered topography is to use Easel's greyscale feature where you fill each layer with a different shade of grey. Easel cuts the depth dependant on the % black. I use inkscape to create the svg then import to Easel. For editting the topography I use QGIS whch can handle any map data and export to svg.