So I'm finally ready to rout a large site model and am looking for any pertinent advice anyone has to offer. I've seen the other threads on the subject, but wanted to ask specifically about materials/process/finishing. Should I plan to rout the topography out of pink insulation foam and skim coat it with plaster? modeling paste? gesso? Should I use a scrim to prevent cracking? How should I sand the model once I've coated it (or should I sand it before I coat it)?

Any information/advice would be very much appreciated... but I'm also interested in what anyone may think about the broader implications of a model like this. My professor is hesitant about making the model any other way besides layered chipboard, but that seems ridiculous to me considering the size of the model (3x6 feet) and the limitations of the laser cutter... The way he sees it, we rely on abstracted topographic models to understand the represented landscape ("its just a language we understand"), but I think thats just an excuse for his reticence to try out the school's new technology. Any thoughts?