A cut edge or a bounding box around a relief map creates cross-sectional profiles through the topography. The edges give additional reference points in visualising the lie of the land and for comparing relative distance, elevation and gradient.

Relief map of the Cairngorm moutains machined in Polyurethane model block - The Cutting Room, CNC Routing
Sources and further information
http://www.liefooghe.be/indexb.php?project=20
http://www.netwerk-art.be/en/activities/exhibitions/19
http://www.awm.gov.au/blog/2007/07/13/relief-maps-of-the-western-front
http://www.cncrouting.co.uk/gallery/raised-3d-relief-map.htm