Digital Elevation Models
A representation of terrain elevations for geographic digital information.
Digital Elevation Models (DEM) represent a significant evolution in the mapping and graphical representation of geographical data. Characterized by their ability to illustrate the terrain of a geographical area in a digital format, DEMs provide a three-dimensional view of the earth's surface, helping researchers, developers, planners, and scientists understand the topography of an area.
DEM is used to create relief maps and serves as a data input for several direct survey procedures. They provide quantitative heights for the field where they are represented and are extensively used in Geographic Information System (GIS) and for preparing topographic maps.
The primary DEM data format is raster, a grid of cells or pixels organized into rows and columns. Each cell in the raster represents a square of the Earth's surface, and the value of the cell corresponds to the average elevation of that square. The size, or resolution, of the cell determines the level of detail in the DEM: a smaller cell size will yield more detailed geographic features, while a larger cell size will offer a broad overview of the landscape.
However, the raster is not the only data format for DEM. There's another format known as TIN (Triangular Irregular Network) which represents the Earth's surface as a set of contiguous, non-overlapping triangles. Compared to the raster format, TIN offers greater detail and more accurate representation of changes in land surface elevations but has larger storage requirements and complex algorithms for generating TIN are needed.
The DEM data are generally provided in two different types. There are 1 arc-second DEM (approximately 30 meters resolution) and 1/3 arc-second DEM (approximately 10 meters resolution). The former is the regular DEM that provides a high-level view of the topography, while the latter is a High-Resolution DEM that provides a more detailed understanding of the landscape.
DEM data are typically sourced from a variety of remote sensing methods such as aerial photography, interferometric synthetic aperture radar (IfSAR), Lidar, and other satellite imaging technologies. The reliability and accuracy of DEM data can vary greatly depending on the method of collection.
GIS software applications can import and utilize DEM data in several different formats including .DEM, .DTED, .SDTS, and .TIF among others. Each of these formats, while maintaining the fundamental aspects of digital elevation modeling, offers unique characteristics that make it more suitable for certain types of GIS-related tasks.
In summary, Digital Elevation Models allow for accurate and detailed representation of terrain in a digital format. This data is shifting the way we visualize, analyze, and interpret the physical world around us. By working with Digital Elevation Models, GIS experts are able to take geographical data to a new level—in a literally elevated sense.
