Integrated Land Change Monitoring

Because so many other statistics and phenomena are reported and mapped on a county basis, they are a useful accounting unit with which to view the occurrences of topographic change. The counties that contain topographic change polygons are shown below. A total of 1,170 counties contain change polygons, which represents 37.6 percent of the counties in the conterminous United States. In some states...

Ecoregions have been developed and are being used to study the place dependency of environmental processes, including anthropogenic transformations of the land surface. Ecoregions are also the basis for reporting on the status and trends of land cover and land cover change. As a geographic framework that is useful for studying the response of the environment to human activities, ecoregions form a...

Because they are a natural partitioning of the land surface, watersheds have been used extensively to study and report on environmental conditions. As such, they provide another useful way to view and present the extent of topographic changes. The connectivity of watersheds may be an important condition when assessing the impacts of land surface transformations. For instance, an important...

The spatial distribution of the topographic change polygons across the states is shown in the figure below. Some noteworthy patterns seen on the map are a dense concentration of polygons in eastern Kentucky and southern West Virginia, a distinct cluster of polygons in northern Minnesota, several larger groups of polygons in Wyoming and southern Arizona, a concentration of polygons in the highly...

Topographic change due to landfill operations has been observed based on some of the features delineated by the elevation differencing and thresholding process. The resulting altered landforms from landfills differ from other anthropogenic activities in that much of the deposited material is not rock and soil that had been previously excavated but man-made material that has been transported to the...

Hydrologic interference is a primary direct anthropogenic process, and dam construction is one type of interference that usually has obvious effects. Certainly, earth materials are moved during dam construction, but the larger impact is the inundation by the reservoir behind the dam.

The importance of urban development (including building construction and associated road construction) as a human geomorphic process has been recognized as a primary input for calculations of the total amount of material moved by humans. The topographic change polygon dataset includes many features that are the result of earth-moving operations for urban development.

Road construction is one of the primary activities in which humans move large quantities of earth materials. The importance of road construction as a major anthropogenic process is evidenced in the literature in its use as one of only a few factors to calculate the total human geomorphic impact on the environment. Case studies indicate that the cuts and fills required to create flat ground for...

The final delineation of topographic change polygons included 5,263 distinct features, representing both cuts (decreased elevations) and fills (increased elevations). In addition, 364 polygons outline areas of reservoir construction or expansion, or other similar hydrologic land uses. Each of these polygons has numerous attributes that describe the specific surface modification, such as area and...

The output of the differencing and thresholding procedures described above was a set of pixels with elevation differences large enough to be judged significant. Ideally, these differences would represent the set of true topographic changes that could then be used for further analysis. In reality, this was not the case, as the selected differences included areas that clearly did not reflect...

The next step in the data processing procedure was to threshold the difference grids to isolate areas of significant change. This procedure is commonly done in the image differencing method of change detection, and the threshold is often based on the standard deviation value of the differences. As implemented for this study, the thresholding approach incorporated the inherent absolute vertical...

The thresholding approach (described below) used to distinguish significant differences from the raw difference grids requires a measure of the absolute vertical accuracy of each input elevation dataset. The NED and SRTM data were compared to an independent reference geodetic control point dataset from NGS. These points have centimeter-level accuracy in their horizontal and vertical coordinates...