GIS Files 1: Getting to grips with GIS

1.2: Introducing raster and vector (3)

Raster data

In raster data the entire area of the map is subdivided into a grid of tiny cells. A value is stored in each of these cells to represent the nature of whatever is present at the corresponding location on the ground. Raster data can be thought of as a matrix of values.

The major use of raster data involves storing map information as digital images, in which the cell values relate to the pixel colours of the image. In the example above the data records the colour of the feature which occupies that part of the map surface; the values recorded in the cells are either white, blue or red. To reproduce the image the computer reads each of these cell values one by one and applies them to the pixels on the screen.

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