Classification and Legend
the classification is an abstract representation of the situation
in the field using well-defined diagnostic criteria: the classifiers.
A classification describes the framework with the names of the
classes and the criteria used to distinguish among them. The
classification requires the definition of class boundaries,
which should be clear, precise, possibly quantitative, and based
upon objective criteria.
A classification should therefore be:
- scale independent, meaning that the classes at all levels of the
system should be applicable at any scale or level of detail;
- source independent, that is independent from the means used to
collect information, weather satellite imagery, aerial photography,
field survey or some combination of them is used.
The legend is the application of a classification in a specific area
using a defined mapping scale and specific data.
Therefore a legend may contain only a proportion, or sub-set, of
all possible classes of the classification. Thus a legend is:
- scale and cartographic representation dependent (e.g. occurrence
of mixed mapping units if the elements composing these unit are too
small to be delineated independently)
- data and mapping methodology dependent (e.g. an aerial photograph
shows features different from those shown by a satellite false colour
composite image).
