Lecture 12 : Terrain Mapping (Link to Powerpoint file)

Lab 13 : Terrain Mapping

Terrain Mapping and Analysis

Terrain mapping generally used on surface elevation data
Elevation data models
Contour maps
Traditional cartographic method of displaying terrain data
Digital Elevation Model (DEM)
Data stored in grid format
Triangulated Irregular network (TIN)
Divides land up into a series of non-overlapping triangles
More compact modeling than DEMs but some loss of information

Elevation Data Models (cont.)

Contour maps
Traditional cartographic method of displaying terrain data

Digital Elevation Model (DEM)
Data stored in grid format
Precision of the DEM depends on the grid cell size
Smaller grid cells yields a more precise DEM but also larger file sizes

Triangulated Irregular network (TIN)
Divides land up into a series of non-overlapping triangles
More compact modeling than DEMs but some loss of information

Contours vs. DEMs vs. TINs

Contour Advantages
Contour maps exist for basically anywhere in world
Contour data are easily interpretable by map readers
DEM Advantages
Simple grid model
Provides uniform coverage over the study area
Computationally more efficient/simple for terrain analysis by computers
TIN Advantages
Takes less storage space
Can create from a sample of survey points (don’t need full coverage)
Can add new elevation points as they become available
Can distribute elevation point selection where they will be most useful

Contour Disadvantages
Data quality is limited by the choice of contour interval
Data are difficult to use for advanced terrain mapping techniques
DEM Disadvantages
Data are hard to visually interpret by map readers
Data quality is limited by the choice of grid cell size
Data sets can become very large
TIN Disadvantages
Can tend to hide important intermediate elevation points

Terrain Data Acquisition

Simplicity of the DEM data model makes it the predominant data format of current elevation data setsTerrain Mapping Techniques
DEM data sources
Occasionally DEMs are created from manual contour maps
Aerial photogrammetric Interpretation
Using stereoscopic techniques DEMs can be semi-automatically created from aerial photograph coverages
Airborne sources
Using Infrared and Radar technology, elevation data sets can be captured by equipment carried onboard aircraft or satellites.

Terrain Mapping Examples

Contouring
Most common and traditional technique for elevation mapping
Hypsometric Tinting
Applies different colors to different elevation zones
Hill Shading
Simulated 3-D view by positioning a hypothetical light source.

Perspective View
Sophisticated creation of a 3-D view from a given vantage point
Vertical Profiling
Demonstrates the change in elevation over a given path

Terrain Analysis

Terrain Analysis Techniques
Slope
Slope measures the rate of elevation change between adjacent cells
Aspect
Aspect measures the direction the slope faces
0° = North facing slope, 90° = East, 180° = South, 270° = West
Sometimes reclassify aspect down to the 4 or 8 principal directions
Viewshed Analysis
Viewshed is an estimate of the land that is visible from a given point
Operates on line of sight principles
Watershed Analysis
Delimits the areas that water will drain to