1. Terrain Mapping and Analysis
Chapter 12

2. Introduction Terrain mapping Land surface is 3-D
Elevation data or z-data is treated as a cell value or a point data attribute rather than as a coordinate.

3. Data for Terrain Mapping and Analysis
Digital Elevation Model (DEM)
Array of elevation points
7.5 minute USGS quads into 4 levels
Level 1 RMS 7-15 meters
Level 2 RMS of ½ contour interval
Level 3 RMS of 1/3 contour interval not to exceed 7 meters
What happened to Level 4?
Relative and absolute errors

4. Data for Terrain Mapping and Analysis
Triangulated Irregular Network (TIN)
Series of non-overlapping triangles
Elevation values are stored at nodes
Irregular distribution
Sources: DEMs, surveyed elevation points, contour lines, and breaklines
Breaklines are line features that represent changes of the land surface such as streams, shorelines, ridges, and roads

5. Data for Terrain Mapping and Analysis
Triangulated Irregular Network (TIN)
Not every point in DEM is used
Only points most important
VIP (Very Important Points) algorithm
Maximum z-tolerance algorithm
Delaunay triangulation: all nodes are connected to their nearest neighbor to form triangles which are as equi-angular as possible.
Borders are a problem
Go beyond study area and clip to make best

6. Terrain Mapping Contouring is most common method for terrain mapping
Contour lines connect points of equal elevation (isolines)
Contour intervals represent the vertical distance between contour lines.
Arrangement of contour lines reflect topography

7. Terrain Mapping
Vertical profile shows changes in elevation along a line, such as a hiking trainl, road or stream.

8. Terrain Mapping
Hill shading is also known as a shaded relief or simply shading
Attempts to simulate how the terrain looks with the interaction between sunlight and surface features.
Helps viewers recognize the shape of land-form features on a map.
Digital shaded-relief map of US

9. Terrain Mapping Four factors control the visual effect of hill-shading
Sun’s azimuth is direction of incoming light (0 to 360°)
The sun’s altitude from horizon (0-90°)
Surface slope (0-90°)
Surface aspect (0 to 360°)

10. Terrain Mapping Hypsometric tinting
Applies different color symbols to represent elevation zones.

11. Terrain Mapping Perspective View 3-D draping of vector information
Perspectives are 3-D views of the terrain wherein the appearance is as viewed from an airplane.
Viewing azimuth (0 to 360°)
Viewing angle (0-90°)
Viewing distance
Z-scale is ratio between he vertical scale and the horizontal scale (exaggeration factor)
3-D draping of vector information

12. Terrain Analysis
Slope measures the rate of change of elevation at a surface location
Aspect is the directional measure of the slope (degrees- 4 or 8 directions)
Important for analyzing an visualizing landform characteristics
Accuracy an issue
If you want to try, use the worked examples in the text with Excel

13. Terrain Analysis Surface curvature: convex or concave
Viewshed analysis
Viewshed refers to the areas of the land surface that are visible from an observation point or points.
Watershed analysis
Watershed is an area that drains water and other substances to a common outlet

14. Terrain Analysis Watershed analysis
Requires three data sets in raster format
Filled elevation grid
Flow direction grid
Flow accumulation grid

15. Grid vs TIN Different algorithms and type of output
Can be converted from TIN to grid or grid to TIN
TIN has flexibility of input sources: DEM, breaklines, contour lines, GPS data and survey data as well as user added elevation points.
Elevation grid is fixed with a given cell size

16. Grid vs TIN Computational efficiency with grid TIN gives sharper image
How are they built and used?