Even when they are not split? If the vertices are welded, they'll hold together when displaced. For things with sharp angles, it won't necessarily look good (especially with extreme displacement), but the faces shouldn't detach. Welded things shouldn't leave a gap. >> Do the polygons keep their exact size, or do the polygon vertices just move according to their normal vector? Everything gets moved outward (or inward, for negative displacement) along the normal vectors. This can result in expansion or compression of the displaced mesh. Yes, for all extents and purposes, the polygons effectively change size. The polygons are also subdivided, as necessary, to accommodate additional geometric detail as defined by the displacement map.