Topographic Mapping

Subtitle

What is topographic mapping?

Topographic mapping is the science of collecting and displaying surface shape and elevation data. Some methods of collecting this data include radar, LIDAR, and photogrammetry.

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Topographic data can be displayed in many ways, depending on the purpose. It is important to remember that all maps use interpolation, meaning that known elevation values at various points are connected by inferred lines or curves created by humans or computers. The closer together that measured points are (higher resolution), the less potential for error is present between points. Here are some examples of topographic maps:

Wireframe and 3-D perspective models

When elevation data is first collected, the points at which is it has been collected are often plotted in a 3-D computer model and connected with lines that are estimated using various algorithms. This results in a wireframe projection (a). The wireframe projection can then be used to create other kinds of maps, like the ones shown below. One such map is a 3-D perspective view (b), which simply involves draping a digitized fabric over the projection to create a surface. This fabric is sometimes based on visible imagery of the area to create a 3-D image that represents the area both topographically and spectrally so that it looks almost like the map reader is at the location. These 3-D representations are best viewed on a computer so that the view can change the view angle by toggling around.

Image credit: Hirano et al. 2003

Contour Map

A contour map uses lines to connect points of equal elevation. Shadowing is sometimes used, with a hypothetical light source in the northwest because an illusion of inversion results if the light source is in the southeast. They are useful for displaying elevation on a printable, portable, 2-D map and are useful for hiking, geology, marine navigation (bathymetric topo maps), and many other purposes. They often include reference data like raods and trails. 

Image credit: Caltopo

Colorized terrain map

Some maps use a color scheme to represent elevation. This can create a smoother-looking map showing a continuous slope. It is particularly useful for large areas that are mostly flat or shallow-sloping but have some extremely steep slopes bounding areas of different elevations. If contour mapping was used, the lines would either be so dense in some parts of such maps that they would appear as a single thick line, or the contour interval would have to be so sparse that the lines would not convey much useful information. One such area is shown below: the nearly flat Tharsis Plateau on Mars with steep-walled canyons and depressions as much as 8,000m deep!

Image credit: Google Earth

Sources

Brock, John C., and Samuel J. Purkis. "The emerging role of lidar remote sensing in coastal research and resource management." Journal of Coastal Research (2009): 1-5.

Harding, David J., and Gregory S. Berghoff. "Fault scarp detection beneath dense vegetation cover: Airborne lidar mapping of the Seattle fault zone, Bainbridge Island, Washington State." (2000). 

Hirano, Akira, Roy Welch, and Harold Lang. "Mapping from ASTER stereo image data: DEM validation and accuracy assessment." ISPRS Journal of Photogrammetry and Remote Sensing 57.5 (2003): 356-370.

Hodgson, Michael E., et al. "An evaluation of LIDAR-and IFSAR-derived digital elevation models in leaf-on conditions with USGS Level 1 and Level 2 DEMs." Remote sensing of environment 84.2 (2003): 295-308.

Lorenz, R. D., et al. "The sand seas of Titan: Cassini RADAR observations of longitudinal dunes." Science 312.5774 (2006): 724-727.

Neumann, Gregory A. "Some aspects of processing extraterrestrial LIDAR data: Clementine, NEAR, MOLA." International Archives of Photogrammetry and Remote Sensing 34.3 (2001): W4.

Sandwell, David T., et al. "New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure." Science 346.6205 (2014): 65-67.