md` Thematic maps are specialized maps made to visualize a particular subject or theme about a geographic area. Thematic maps can portray physical, social, political, cultural, economic, sociological, or any other aspects of a city, state, region, nation, continent, or the entire globe.^{[[1](http://www.lib.washington.edu/maps/MapResources/thematic2.html "Thematic Maps Map Collection & Cartographic Information Services Unit. University Library, University of Washington.")]} These maps are designed to illustrate a particular subject, and can accomodatrea variety of phenomena appearing together, such as landforms, lines of transportation, settlements, and political boundaries.^{[[2.1](# "Norman Joseph William Thrower \(2007\). Maps & Civilization: Cartography in Culture and Society. p.95.")]} While features such as coastlines, boundaries and places offer points of locational reference for the phenomenon being mapped,^{[[2.2](# "Norman Joseph William Thrower \(2007\). Maps & Civilization: Cartography in Culture and Society. p.95.")]} it is important to acknowledge that the data being represented are abstrated, and their locational point of reference is typicaly an arbitrary choice. In this case, population is used to proportionally vary the size of a circle marker (a "[bubble](https://observablehq.com/@d3/bubble-map)"), and the bubble location is calculted at the center of the polygon it represents. A force method is apply to prevent overlapping bubbles. This kind of cartograms are popularly knowns as _Dorling cartogram_. You can find many such examples, like [Dorling Cartogram by Harry Stevens](https://observablehq.com/@harrystevens/dorling-cartogram), in Observable. `