2.2.2 Raster data structure

Raster layers represent continuous features such as aerial and satellite imagery, as well as Digital Elevation Models (DEM), which store elevation data across a surface (see section 3.2.4. for more information). The value of each pixel of a thematic raster layer represents the attribute value. For satellite imagery, pixel values represent physical values of surface reflectances and for terrain-model data pixel values represent absolute topographic heights (Campbell, 2002). For example, if the resolution of the image is 25 m, then each 25 m pixel in the image will be representative of the average value of that 25 m on the ground. In Fig. 3, a land cover vector layer was transformed to a raster to visualize the pixel differences and value types.

Fig. 3. A map displaying the raster data structure of a landcover layer which was converted from vector format. The legend denotes the landcover properties which are displayed. Reproduced with permission of Swisstopo (BA13016).