GIS Files 1: Getting to grips with GIS

1.2: Introducing raster and vector (2)

Vector data

In vector data the features are recorded one by one, with shape being defined by the numerical values of the pairs of xy coordinates.

A point is defined by a single pair of coordinate values.
A line is defined by a sequence of coordinate pairs defining the points through which the line is drawn.
An area is defined in a similar way, only with the first and last points joined to make a complete enclosure.

Vector data can be thought of as a list of values.
In the example above the map represents a building as a simple red rectangle. In vector data the position and shape of the building is captured as a series of four pairs of numerical coordinates. To reproduce the building in a GIS the computer reads these values and draws a line linking the coordinate positions. The vector version can also store additional context information about these features – the attributes – a very important aspect, which will be explained in later chapters of the GIS files.

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