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Types of objects

Continuous fields
- elevation, rainfall
- represented by raster data model
Discrete objects / features
- lines, points, areas with attributes
- represented by vector data model as geometry with attribute table or object based
- can be also represented by raster data model (streams, roads, landuse??? - we have vector, but whatever)

DEM

is a digital model or 3D representation of a terrain's surface created from terrain elevation data
DEM can be represented as a raster (a grid of squares, also known as a heightmap when representing elevation) or as a vector-based triangular irregular network (TIN). The TIN DEM dataset is also referred to as a primary (measured) DEM, whereas the Raster DEM is referred to as a secondary (computed) DEM.[9] The DEM could be acquired through techniques such as photogrammetry, lidar, IfSAR, land surveying, etc.