377
Digital Landscaping
Digital Topographic Maps, Contours, Digital Terrain Modeling,
Digital Elevation Models (DEMs), NED, SRTM, LIDAR, and 3D
Views of Landscapes and Terrain
13
Part 4 Geospatial Applications
377
There’s one big element missing in geospatial technology that we haven’t yet
dealt with: the terrain and surface of Earth. All of the maps, imagery, and coordinates (while taking into account numerous critical features of the planet)
have been dealing with two-dimensional (2D) images of the surface or of developed or natural features on the land. We haven’t yet described how the actual landscape can be modeled with geospatial technology. This chapter delves
into how terrain features can be described, modeled, and analyzed using several of the geospatial tools (like GIS and remote sensing) that have been previously described. Whether you are modeling topographic features for construction or recreational opportunities, or interested in seeing what the view from
above would be, the landforms on Earth’s surface are a necessary component
of geospatial analysis (see Figure 13.1 on page 378 for an example of visualizing Mount Everest with Google Earth).
First and foremost, when we’re examining landforms on Earth’s surface,
each location will have to have an elevation assigned to it. In terms of coordinates, each x/y pair will now have a z-value accompanying it that indicates
that location’s elevation. These elevations have to be measured relative to
something—when a point has an elevation of 900 feet, this indicates that it is
900 feet above something. The “something” represents a baseline, or vertical
datum, that is the zero point for elevation measurements. Some maps of landforms indicate the vertical datum is taken as mean sea level ( represented by
the National Vertical Datum of 1929). Thus, when this vertical datum is used
and an elevation value on a map indicates 1000 feet, that number can be read
as 1000 feet above mean sea level. Other geospatial data in North America
utilizes the North American Vertical Datum of 1988 (NAVD88). Coastal terrain models may also use mean high water.
z-value the elevation
assigned to an x/y
coordinate.
vertical datum
a baseline used as
a starting point in
measuring elevation
values (either above or
below this value).
Digital Landscaping
Digital Topographic Maps, Contours, Digital Terrain Modeling,
Digital Elevation Models (DEMs), NED, SRTM, LIDAR, and 3D
Views of Landscapes and Terrain
13
Part 4 Geospatial Applications
377
There’s one big element missing in geospatial technology that we haven’t yet
dealt with: the terrain and surface of Earth. All of the maps, imagery, and coordinates (while taking into account numerous critical features of the planet)
have been dealing with two-dimensional (2D) images of the surface or of developed or natural features on the land. We haven’t yet described how the actual landscape can be modeled with geospatial technology. This chapter delves
into how terrain features can be described, modeled, and analyzed using several of the geospatial tools (like GIS and remote sensing) that have been previously described. Whether you are modeling topographic features for construction or recreational opportunities, or interested in seeing what the view from
above would be, the landforms on Earth’s surface are a necessary component
of geospatial analysis (see Figure 13.1 on page 378 for an example of visualizing Mount Everest with Google Earth).
First and foremost, when we’re examining landforms on Earth’s surface,
each location will have to have an elevation assigned to it. In terms of coordinates, each x/y pair will now have a z-value accompanying it that indicates
that location’s elevation. These elevations have to be measured relative to
something—when a point has an elevation of 900 feet, this indicates that it is
900 feet above something. The “something” represents a baseline, or vertical
datum, that is the zero point for elevation measurements. Some maps of landforms indicate the vertical datum is taken as mean sea level ( represented by
the National Vertical Datum of 1929). Thus, when this vertical datum is used
and an elevation value on a map indicates 1000 feet, that number can be read
as 1000 feet above mean sea level. Other geospatial data in North America
utilizes the North American Vertical Datum of 1988 (NAVD88). Coastal terrain models may also use mean high water.
z-value the elevation
assigned to an x/y
coordinate.
vertical datum
a baseline used as
a starting point in
measuring elevation
values (either above or
below this value).