Categorization: The transformation of continuous values to distinct values. This is
for example needed to generate choropleth maps from continuous attributes.
Another example would be the stepwise selection of different text heights or line
widths in dependence from such an attribute.
In case the Categorize (or Interpolate) function is used inside a RasterSymbolizer as a
ColorMap, the LookupValue is set to the fixed value “Rasterdata”.
The Thresholds have to be specified in ascending order and (like the LookupValue)
have to be of a uniform and orderable type. The value of the function is determined by
looking up into which interval between two thresholds the LookupValue falls. The first
interval ranges from -Infinity to the first given threshold and the last one accordingly
from the last threshold to +Infinity.