GEOG
361, C. Brewer
Map Generalization
Reading: Krygier and Wood, first
half of Ch 8 (pp 145-151)
Abstract
the infinite complexity and diversity of the real world into a
cartographic representation targeted for use for a given map purpose
and scale range (Müller and Wang)
When to generalize (McMaster):
congestion, coalescence, conflict,
complication, inconsistency, imperceptibility
How to generalise:
Early model
(Robinson et al.): select, simplify, classify, symbolize
Operations (Roth et
al.):
Content:
Selection (Add) - choose the categories to
include on the map*
Eliminate - removal of features
Reclassify - revision to the grouping of features
based on their attributes
Geometry:
Simplify - reduction of the
number of points constituting a feature (most research done on this
vector operator)*
Aggregate -
replacement of many related features with a
representative feature of increased dimensionality (dimension change)*
Collapse - replacement of a feature with a representative
feature of lower dimensionality (dimension change)*
Merge -
replacement of a feature with a representative feature
of equal dimensionality
Displace -
adjustment to the location of a feature to avoid
coalescence with adjacent features while maintaining topology*
Exaggerate - amplification of a portion of a feature to
emphasize a characteristic aspect of it
Smooth -
removal of small variations in the geometry of a feature to improve its
appearance*
Symbolize
Enhance - inclusion of graphic embellishments around or within
a feature to maintain or emphasize feature relationships*
...
* also in Krygier and Wood
Example simplification algorithms:
Douglas-Peucker (Poiker), Visvalingham...
Demonstration tool: Mapshaper.org