Pattern Recognition and Typification of Ditches - Advances in Cartography and GIScience - page 429

3- Characterization of ditches
As the Oxford dictionary defines it, a ditch is "a narrow channel dug at the
side of a road or field, to hold or carry away water". Ditches are man made
features used to convey water; they are typical of rural environments,
where they may run along the roads or inside the fields, eventually divid-
ing different crops. Ditches can be dug singularly, but most often are made
in groups, for example as part of an irrigation or drainage system. Being a
man made feature, ditches usually show a regular pattern: groups of
ditches often run parallel to each other, in straight lines with similar
lengths and equally spaced (see Figure 1 ).
From the cartographic point of view, ditches are represented as single lines
that might or might not be connected to other features of the hydrology
network; ditches usually do not take part in the hydrology graph and as
they are usually not described with a rich semantic they are treated as a
different feature class than rivers and canals.
Figure 1: on the left: ditches not connected to any other feature; on the right: ditches are
connected to other hydrographic features; in both figures the regularity of the patterns is
noticeable.
In rural environments, characterized by the absence of dense road networks or settle-
ments, the straight patterns of ditches are a prominent feature and as such they should be
retained during generalization. It is interesting to underline though, that what is important
to the description of the rural landscape is not the single straight ditch but the pattern of
the group as a whole. Because of this, ditches lend themselves to be typified.
Selection vs. typification
One may wonder whether there really is the need of a typification algo-
rithm to generalize ditches, or a simple selection algorithm could do the