6.9.4. Applying a colour map

The layer g100_06_ch_FR.tif is now an efficient size for our analysis, but we still do not know what the numbers (raster values) in the raster represent (see Fig. 50). This is due to the fact that the attribute table of the g100_06.tif layer does not include the official CLC06 land cover codes because of a purely technical reason: the codes (50 in total) range from 111 to 999 and cannot be displayed in a single band 8-bit integer raster dataset because the range of values is limited to 0-255. Of course a 32-bit floating-point raster image could be used to display the whole range of values from 111 to 999. However, this would almost quadruple the size of the dataset which would cause problems for download, storage, and analysis. For this reason, the European Environment Agency (EEA) provides a layer file along with the raster image to indicate the code and colour map information which can be easily integrated into ArcGIS.

To add the code and colour map information:

  1. Browse to the unzipped land cover folder (g100_06.tif).
  2. Add the clc_colortable_92.lyr file to ArcMap (section 6.3.3.).
  3. In the TOC, you should now see a layer called: lceugr250_00_pct.tif (which corresponds to the clc_colortable_92.lyr file) with a red exclamation point (!) beside it. That means that the layer does not know where the data are located. The codes (e.g. 111, 112, etc.) in this file represent the land covers type from the CLC06 dataset.
  4. Right-click the lceugr250_00_pct.tif layer.
  5. Click Data.
  6. Now click Repair Data Source to tell the layer where the data are located.
  7. Browse to the g100_06_ch_FR.tif layer.
  8. Click Add. The red exclamation point beside lceugr250_00_pct.tif should have disappeared.