Abstract
Cartographic generalization research has focused almost exclusively in recent years on topographic mapping, and has thereby gained an incorrect reputation for having to do only with reference or positional data. The generalization research community needs to broaden its scope to include thematic cartography and geovisualization. Generalization is not new to these areas of cartography, and has in fact always been involved in thematic geographic visualization, despite rarely being acknowledged. We illustrate this involvement with several examples of famous, public-audience thematic maps, noting the generalization procedures involved in drawing each, both across their basemap and thematic layers. We also consider, for each map example we note, which generalization operators were crucial to the formation of the map’s thematic message. The many incremental gains made by the cartographic generalization research community while treating reference data can be brought to bear on thematic cartography in the same way they were used implicitly on the well-known thematic maps we highlight here as examples.
Highlights
People outside the discipline and students early in their studies are often surprised to learn that mapmakers willfully filter and modify the information included on any given map in the interest of clarifying the overall message
The elemental techniques used in generalization of geospatial data or map symbols for geographic entities are termed operators [4], and numerous typologies of these have been defined throughout recent years
These and other gains made by the cartographic generalization research community while treating reference data can be brought to bear on issues in thematic cartography, including the visualization and sense-making of massive, heterogeneous datasets
Summary
People outside the discipline and students early in their studies are often surprised to learn that mapmakers willfully filter and modify the information included on any given map in the interest of clarifying the overall message. Omission of things and places on maps is perhaps one of the first things people become aware of when they learn this, giving them a new appreciation of the saying about how some event caused some place to be “put on the map” They may further learn that roads, coastlines, or borders are more complex than the lines drawn for them, and might even be displaced from their actual location to avoid symbol overlaps. Aside from mistakes or intentional falsehood [2], we know that these disparities with reality are caused by generalization, and that this is entirely necessary for human understanding and the limitations of graphic resolution at map scales, among other reasons. Our thesis comes as the map generalization research community is awakening to the importance of the broad world of thematic cartography lying outside of the topographic and reference map realm it has recently been focused on
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