The digital elevation model in GIS describes as the elevation information of the earth's surface(relief), moon, and asteroid in the digital format. This digital format is called the digital elevation model(DEM).
The DEM is a computerized representation of the earth relief in different formate such as triangulated irregular networks (TIN), regular grids, contour lines, scattered data points. The digital elevation model is presented by wireframe model and image matrix.


The currently available digital elevation model exhibit discontinuities with respect to coverage resolution, accuracy, and reference datum, they are also inhomogeneous because they are derived through different methods. The currently best, most comprehensive, global data set comes with a horizontal resolution of one kilometer and elevation accuracy of 100 meters.



           The no. of methods available for obtaining elevation data for DEM.

(a) LIDAR:-Lidar is a method for determining ranges by targeting an object with a laser and measuring the time for the reflected light to return to the receiver lidar can also be used to make a digital 3D representation of an area on the earth surface and ocean.
(b) Radar:-Radar is a detection system that uses radio waves to determine the object's range, angle, or velocity. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles.
(c)Ariel survey:-Aerial survey is a method of collecting imagery data by using airplanes, UAVs, and other aerial methods.
(d)Real-Time Kinematics GPS:-The Global Positioning System is satellite-based navigation and surveying system to determine precise position and time.
It is work in three segments.
1. Space Segment.
2. Control Segment.
3. User Segment
(e)Topography Survey Map:-Topography survey is the process of determining the position, both in plan and elevation of the natural and artificial features of the region with conventional symbols.

(f) Total Station survey:-Total Station is an electronic or optical instrument for measure angle, distance, and coordinates. It is a combination of transit theodolite with an electronic distance meter.
(g) Doppler Radar:-A Doppler radar is a specialized radar that uses the doppler effect to produce velocity data.

                   Relation between DEM and Geographical Information Systems
DEM can be used together with other spatial data, image data in a geographic information system. The DEM provides a basic spatial reference system to the GIS spatial data set images or vector information can automatically be draped over and integrated with the DEM for more advanced analysis.

                                Application of data elevation model

Nowadays DEM has played an important role in the analysis result, product development, and decision making.
1. Scientific application:-The scientific application of DEM is about the surface of the earth.
DEM has used for the study of topography and the shape of the earth. Another area of application is global land cover classification, precise mapping of and classification of the earth surface.

A. Climate impact studies
B. Water and wildlife management
C.Geological and hydrological modeling.
D. Geomorphology and landscape analysis.
E. Mapping purposes
F. Educational programs.

2. Commercial application:-Commercial applications are more market and business-oriented applications related to the sale and distribution of DEM and DEM products.
B.Air traffic routing and navigation
C. Planning and Construction
D.Hydrological and meteorological services.
E.Geo-coding of remote sensing
F.Market of multimedia applications and computer games.

3.Industrial Applications:-For industrial applications digital elevation models are used for the development of the market-oriented product technology, improved services and to increase the economic outcome of productions.

A. Telecom

4.Operational Applications:-The geo-information data is used in all types of government planning, administration, and management. The DEM is used for the improvement of planning and management of natural resources and within the area of regional planning, environment protection, hazard reduction, military, and other security-relevant application, insurance issues, health services, agriculture, forestry, and soil conservation.   

The data structure for a continuous surface model of three-dimensional shape. The surface model is used for creating a grid at regular intervals, random points, contour lines, and surface profile making.

what is contour and their use
contour lines


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