Geography Reference
In-Depth Information
Map scale can be determined by comparing the distance between two features
on two maps, when the scale is known for one map.
maps. The distances between lines of longitude or latitude can be deter-
mined from tables published on the Internet.
Comparing distances between the same features on two maps when the
scale of one map is known is the third technique. Needless to say, great care
has to be taken when making measurements.
Generalization
To cartographically represent things and events, they must be abstracted to fit
the target scale or scales and still accurately retain key properties and relation-
ships. Just as scale is an indicator about the amount of detail in a map, it is also
an indicator about the amount of
generalization
, the abstraction of features to
reduce complexity in maps or geographic information. Generalization serves
to assure that cartographic communication works as well as possible at a partic-
ular scale or scales. Scale first defines the relationship between an area on the
ground and an area on maps or in visualizations; second, scale constrains the
possibilities for showing things, events, and relationships.
Generalization is often the most important part of cartographic repre-
sentation because it assures the role of the map or visualization for the pro-
cess of cartographic communication. It involves the alteration of GI and sym-
bols. The underlying graphical issue is that with decreasing map scale,
graphical elements (points, lines, areas) will refer to larger things and events.
A square, 1 mm on each side, can represent a playground 25 by 25 m in size
on the ground at a scale of 1:25,000. At a scale of 1:100,000, the same 1 mm
square shows a playground 100 by 100 m large.
Two other issues make generalization necessary. Because the clear carto-
graphic representation of things and events can take up disproportionate
space at smaller map scales, generalization is necessary to avoid cluttering
the map or visualization and to clarify important relationships. Generaliza-
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