Rectangular Cartogram Computation with Sea Regions

In 2004 van Kreveld and Speckmann presented the first algorithms for the automated construction of rectangular cartograms. The first step for these algorithms is to construct a partition of a large rectangle the map into a set of smaller rectangles that represent the regions of the administrative subdivision to be depicted ("countries") as well as (parts of) adjacent oceans, large lakes, or neighboring regions ("sea regions"). Countries have a specified target area that is based on a geographic variable like population. Sea rectangles do not have a specified target area but solely serve to increase the recognizability of the map by preserving a global coast or border outline. In this paper we investigate different ways of partitioning sea regions into rectangles. We also study the effects of different cartographic error measures for sea rectangles. Our experimental results are given both in tabular form and as cartograms, to be able to evaluate both the error and the visual quality.