Abstract: A multitude of parts of three-dimensional shape have full edges and also edge segments adapted for abutment with like edges and edge segments of other parts. The parts additionally include non-abutting irregular or curved edges which may represent terrain contour lines or the bank of a body of water. Inclined areas on the parts are adjacent the irregular or curved edges and represent sloped terrain which is continuous with like inclined areas on other abutting parts. The inclined area of a part may be dispensed with to provide a vertical surface to simulate an escarpment.