A dasymetric dot density thematic map represents quantitative (numerical) data by using dots to show the amount of the mapped phenomena. Each dot is assigned a specific data value and the sum visual total of the dots tells us where there is more or less of the mapped phenomena.
The purpose of the map is to show how areas differ in character which we interpret by viewing the different density patterns formed by the dots. Here, 1 dot = 1 vote so there are over 130 million dots on this map. A red dot represents a Republican vote. A blue dot represents a Democrat vote. There are six zoom scales from 1: 18 million to 1:500,000…zooming in any further leaves vast swathes of emptiness and implies too much meaning to the location of each dot. A popup gets you to the data for each county.
The dasymetric approach does not use typical geographies for displaying population data (such as counties). Here, the election data has been spatially classified using ancillary data to reapportion from one geographic area to another. Voting results at county level are weighted into three urban area classifications (dense urban; urban; and rural) based on the National Land Cover Database classification. The map shows voting patterns as a density of dots in areas where people live and work and overcomes the problem of simply mapping arbitrary geographies, often where no-one lives (or votes!). The knock-on impact is that we see a true pattern emerge which doesn’t distort the visual weight of the relative proportions of red and blue simply by virtue of the size of a geographical area. Dots are positioned randomly within the confines of the extent of the three land use classes and they DO NOT imply the location of individual voters.
The overall effect allows us to see areas where people predominantly vote Republican, or predominantly vote Democrat or where there is a relatively even mix of voting. In the latter case, our eyes deceive us as we tend to see a purple hue because of the close proximity of the red and blue dots. The purple hue tends towards red where Republicans won, and towards blue where Democrats won.