Relief Portrayal

1. Relief Portrayal January 23, 2006 Geog 258: Maps and GIS

2. 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)

3. 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

4. Contours • Think of contours as lines obtained by cutting terrain horizontally with imaginary planes in equal intervals • Contours are lines of equal elevation

5. Types of contours • What would terrain look like inside depression contour? • Not all contours are labeled: index contour is labeled, shown as thick lines

6. What is contour interval from this map?

7. Isobaths • Lines of equal water depth Further questions: Any difference compared to contour map?

8. Hypsometric tinting • Space between contour lines is color-coded Does this look better than a contour map? Why do you think so?

9. Hypsometric tint Is color coding scheme good?

10. Hypsometric tint

11. Spectral color progression

12. Vignetted hypsometric tints

13. 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

14. Physical model of relief • Physical 3D model of relief Raised relief globes Raised relief topographic map Relief models

15. Perspective views • Creates 3D effect with oblique vantage points

16. Perspective views Landscape drawings

17. Perspective views Fishnet maps (terrain profiles) Block diagram

18. Relief shading • Creates 3D effect using an imaginary light source Shaded relief map Vertical aerial photo

19. 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?

20. Which methods are combined in this map?

21. Which methods are combined in this map?

22. Which methods are combined in this map?

23. Which methods are combined in this map?

24. Which methods are combined in this map?

25. Which methods are combined in this map?

26. Which methods are combined in this map?

27. Which methods are combined in this map?

28. 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/

29. 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