Practical GIS

Vector data model

Vector data, unlike raster data, does not have a fixed layout. It can be represented as sets of coordinate pairs (or triplets or quads if they have more than two dimensions). The elementary unit of the vector data model is the feature. A feature represents one logically coherent real-world object--an entity. What we consider an entity depends on our needs. For example, if we would like to analyze a forest patch, we gather data from individual trees (entities) and represent them as single points (features). If we would like to analyze land cover, the whole forest patch can be the entity represented by a feature with a polygon geometry. We should take care not to mix different geometry types in a single layer though. It is ...