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Q: What are ‘raster’ and ‘vector’?

A: Modern GIS software handles both raster and vector data and both have unique advantages and disadvantages.

Raster

A raster image models geographic features by a collection of grid cells rather like a scanned map or picture. Such data is typically created from scanning paper sources, e.g.: ordnance survey maps, aerial photographs or satellite images. Raster data tends to be relatively high volume and does not possess intelligence, i.e.: the attributes, including geo-referenced location, necessary to be incorporated into spatial analysis. Raster maps are commonly used as a backdrop to the vector layer.

Vector

Vector data are typically described as point, line or area and are particularly suited to sophisticated geographical or spatial analysis. Vector data is intelligent in that the map features are directly linked to the GIS database, so that a selected set of map features (e.g.: brownfield sites, road junctions, location of traffic accidents etc) result from a particular database query.

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