Relief shading involves the use of shadows to emphasize the topography of a terrain. In GIS, most often this involves the use of a digital elevation model (DEM) that has undergone a technique called hillshading. The variation in shadowing gives the elevation a 3D effect and helps put into context how hilly or flat a geographic area is. There are different methods for achieving a shaded relief map and resources for understanding this cartographic technique are listed here.
HillShading
Brief overview of hillshading along with some discussion on hand hillshading and methods. Although the page is dated, it still provides some useful base information.
Hillshading Alternatives
Examples and methodology for creating 3D illusions of terrain using hachure, point symbol and inclined contour techniques.
Relief Shading
Comprehensive site devoted to the techniques of shaded relief maps.
Shaded Relief
Web site of Tom Patterson, from the United States Park Service which presents examples and articles on shaded relief techniques.
Books
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Hillshading of terrain using layer tints with aspect-variant luminosity.(cartography): An article from: Cartography and Geographic Information Science [HTML] (Digital)
by Patrick J. Kennelly (Author), A. Jon Kimerling (Author)
I’ve noticed that it seems common to hillshade with the sun emulated at 315° & 45° above the horizon (or something similar). This doesn’t appear to be good practice relative to real sun angles in the northern hemisphere. I realize using actual figures for the basis of a primarily visual calculation could have downsides (things might literally ‘appear’ to be upside-down). Though this unrealistically illuminates cool northern slopes & shades exposed southern aspects. This is also in direct contrast (quite literally) to the realities of aerial imaging. One can imagine what a transparent overlay of the two would look like (not good). Do standards exist in this regard? Opinions anybody?