A Digital Terrain Model (DTM) is a digital representation of the topography or surface of the earth. It is created by using a series of elevation points or contours and creating a 3D model from them. The elevation data is usually obtained using remote sensing techniques such as LiDAR, which uses lasers to measure the distance between the ground and the sensor.?

DTMs are used in a variety of applications, including urban planning, land use management, and natural resource management. They provide a detailed representation of the land surface, including its slope, aspect, and elevation. This information can be used to identify areas prone to landslides, flooding, or erosion.?

A Digital Surface Model (DSM) is a type of digital elevation model that represents the top surface of the earth, including all natural and man-made features such as trees, buildings, and other structures. In contrast to a Digital Terrain Model (DTM), which represents only the bare earth surface, a DSM includes all features on the earth's surface.