Data Models and Structure
By convention, data in the real world is deemed to exist in a continuous or analogue form usually in three dimensional space as discussed in Sect. 2.1. Such data needs to be digitized or made discrete before it can be input and processed by a digital computer. A GIS database can be viewed as an abstraction of reality. To convert object features observed or measured in the real world into the digital realm in a GIS database it is necessary to structure the data appropriately. Four (4) different generic types of primitive object features can be distinguished, namely: point features (0-D), line features (1-D), area features/polygons (2-D), and surface features (3-D). Incidentally, when surface features are captured in a discrete or non-continuous manner, this is then referred to as 2.5D. In general, an object feature is defined by three (3) properties in GIS, namely: position, attributes and relationship with other features referred to as topology.
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