1.16.6. Digital elevation models (DEMs)

Elevation data form one of the important sources of ancillary data, which is most widely used in Earth-related investigations. The most common form for representation of elevation data in digital format is the grid type or raster format. The elevation matrix consists of a well-known regular grid of elevations representing real topography. Several names are in current use, including Digital Terrain Model (DTM), Digital Elevation Model (DEM), Digital Elevation Data (DED) and Digital Ground Model (DGM).

Digital Elevation Models (DEMs) are computer-readable data representations that show the elevation of the Earth's surface. They are typically arranged in a grid format, where each grid cell contains an elevation value. This type of digital representation helps researchers and planners analyze topographical features and make decisions based on the landscape's elevation. The various names for similar models indicate different focuses - for example, a Digital Terrain Model (DTM) includes more detailed data related to the land features beyond just elevation.

Think of a DEM like a virtual model of a landscape, similar to how video game environments are designed. Just as game developers create detailed backgrounds where characters interact, DEMs create a digital canvas of the real world, allowing scientists to simulate various scenarios, like rainfall runoff or land development.

A DEM is an ordered array of numbers that represents the spatial distribution of elevations above some arbitrary datum in the landscape. It is a numerical representation of the spatial variation in land-surface elevation, which represents the land-surface as a matrix of elevation values (Z) implicitly located by their geographic coordinates (X, Y). Any point in a DEM can be related to its neighboring cells if the data storage is regular.

In a DEM, every point in the grid corresponds to a specific elevation value, organized systematically by geographic coordinates. This means that if you know the coordinates of a location, you can easily find its elevation by looking it up in the DEM. The structured nature of DEMs allows for efficient processing and analysis of geographic information, making it easy to access elevation data for any area.

Imagine a classroom seating chart where each student's name corresponds to a specific seat. Just as you can find out who sits next to whom by looking at the chart, a DEM allows us to find the elevation of a point using its coordinates on the grid.

While DEM consists of an array of values that represent topographic elevations measured at equal intervals on the Earth surface, the Digital Terrain Model (DTM) comprises of any terrain data. A DTM is a topographic map in digital format, consisting not only of a DEM, but also the types of land use, settlements, types of roads and drainage lines and so on.

DEMs focus specifically on elevation data, while DTMs are more comprehensive as they include various types of information about the terrain, such as land usage, road types, and more. This added data makes DTMs particularly useful for urban planning and environmental management, as they provide a fuller picture of the landscape beyond just height.

If thinking of a DEM as a simple recipe that contains only the ingredients (elevation), then a DTM is like a complete cookbook that includes not only the ingredients but also the steps to prepare the dish, cooking times, and serving suggestions. This broader information allows for more informed decisions in planning projects.

DEMs have several applications, which include– (i) Site selection for engineering projects (ii) Analysing and comparing different types of terrain (iii) Selecting the alignment of roads, railways, canals, pipelines, etc. (iv) Cut-and-fill analysis in road design and other engineering projects. (v) Computing terrain parameters (e.g., slope, aspect, profiles, catchment area, etc.) to assist runoff and erosion studies. (vi) Displaying landforms in three dimensions, for design and planning of landscape (vii) Generating drainage network for hydrological studies. (viii) Ascertaining the intervisibility between two points (ix) Improving classifications when combined with satellite data. (x) Storing elevation data for digital topographic maps in national databases.

DEMs are essential in various fields, primarily engineering and environmental science. They help in selecting appropriate sites for construction, analyzing different topographies, and designing infrastructure like roads and pipelines effectively. Additionally, they support studies in hydrology and land development by providing important parameters needed for analysis. The ability to visualize terrain in three dimensions enhances design and planning processes.

Consider a landscape architect planning a new park. They can use a DEM to understand the elevations and slopes of the land, helping them determine the best locations for trails, playgrounds, or water features, similar to how a chef uses a recipe to decide the best combination of ingredients and cooking techniques for a delightful dish.

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