GIS Files 1: Getting to grips with GIS

1.2: Introducing raster and vector (1)

Maps in bits

The first step in converting map information into a form that can be read by a computer is to describe the shapes and locations of features using a series of numbers. Computers store information in sequences of binary digits (bits), which form a code for every possible number or letter.

This fits with the way maps reference geographical locations on the earth's surface, through a system of coordinates. These coordinate systems can be local, national or international. Look at an Ordnance Survey map and you will notice, along the sides, there are a series of numbers associated with a grid covering the whole map area.

These numbers refer to coordinates from the British National Grid. All locations and shapes can be defined in terms of x and y coordinates from a given grid system: it is these numerical values which are used to translate map information into digital form. This applies in both vector and raster formats.

For a complete understanding of how the National Grid works, try the Interactive Guide.

Interactive Guide to the National Grid

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