Relief Portrayal January 23, 2006 Geog 258: Maps and GIS
Outlines How relief is portrayed? • Absolute-relief portrayal methods • Relative-relief portrayal methods • Combining relief portrayal methods • Dynamic relief portrayal Digital data for relief portrayal • DEM (Digital Elevation Model)
1. Absolute-relief methods • Provides relief in a numeric scale • You can determine exact value of elevation or water depth at individual points from this kind of map • Designed to give precise measurements • You can measure slope from this kind of map • You can create profile from this kind of map • Common methods include • Contours: lines of equal elevation • Isobath: lines of equal water depth • Hypsometic tints: color-coded contour interval
Contours • Think of contours as lines obtained by cutting terrain horizontally with imaginary planes in equal intervals • Contours are lines of equal elevation
Types of contours • What would terrain look like inside depression contour? • Not all contours are labeled: index contour is labeled, shown as thick lines
Isobaths • Lines of equal water depth Further questions: Any difference compared to contour map?
Hypsometric tinting • Space between contour lines is color-coded Does this look better than a contour map? Why do you think so?
Hypsometric tint Is color coding scheme good?
2. Relative-relief methods • Designed to give a general impression of relative heights of landform rather than its exact values at individual points • Focused on providing realistic presentation of relief • Different ways to create 3D effect • Commonly used methods include • Physical relief model: raised relief • Perspective view: oblique vantage point • Relief shading: imaginary light source
Physical model of relief • Physical 3D model of relief Raised relief globes Raised relief topographic map Relief models
Perspective views • Creates 3D effect with oblique vantage points
Perspective views Landscape drawings
Perspective views Fishnet maps (terrain profiles) Block diagram
Relief shading • Creates 3D effect using an imaginary light source Shaded relief map Vertical aerial photo
3. Combining relief methods • Absolute methods are good for making measurements, but it is hard to have a general sense of terrain variation • Relative methods are good for gaining a general impression, but it does not give precise measurements • Why not combine both?
4. Dynamic relief portrayal • Putting relief portrayal into motion • Can gain dynamic impression of landform • Animated methods • A sequence of maps is animated detect changes • A series of images taken from different vantage points are combined to create animation fly-over • Interactive methods • You can choose the location, vantage points, and so on • Demo • http://www2.jpl.nasa.gov/srtm/ • http://geology.asu.edu/~reynolds/topo_gallery/topo_gallery.htm • http://www.truflite.com/
5. Digital Elevation Model • Some maps can be made by hand • Relief globe, hachures, block diagram • These days maps are increasingly generated by computers • Shaded relief map, profile map, fly-over • Combining methods are easily manipulated • Basis of computer-generated terrain mapping is Digital Elevation Model (DEM) • DEM stores elevation or water depth in regularly sampled points • DEM can be thought of as varying elevation values stored in matrices