CARTOGRAPHIC LINE GENERALIZATION
In pre-computer times, cartographers and engravers always had the map scales foremost in mind when generalizing map features. Similarly, the automated approach to line generalization we present here depends entirely on the value known as scale ratio (quotient between the generalized and the source map). It is our understanding that in this era of computer Cartography, the scale ratio must play the major role in all kinds of generalizations, thus providing the parameter that would compel algorithms developed for map features as different as buildings, contours, shorelines, streams, roads, and numerical models, to converge into a unified and comprehensive solution.
The solution for the cartographic line generalization we present here was inspired on the 1957 proposal by the Polish mathematician Julian Perkal. The manner of presentation is by the way of application examples. The subjects are large files loaded with all sorts of configurations. All the generalizations were completed successfully without any manual intervention other than the selection of general parameters, such as the scale ratio.
If you are considering a project that might benefit from an automated line generalization, please do send us an e-mail. We are sure that we could accommodate your requirements.
AN ILLUSTRATION OF PERKAL'S PROPOSAL WITH ENHANCEMENTS
a: Original map section
b: The hatched polygons are the areas needing generalization (only shorelines). The epsilon diameter is an expression of the scale ratio.
c: The network in red is the medial-axis of the hatched/yellow polygons.
d: The surplus branches of the medial-axis have been clipped and the stem simplified as well. The result is the generalized shoreline (in red). The streams have been generalized with a similar procedure, adapted to single-sided features.