The author discusses the various issues with creating a choropleth map, which is basically a map in which areas are shaded to represent differing amounts of a variable statistic.
Setting the class intervals can radically change how a map appears, using the same data, therefore its usually helpful to set the intervals so that there is an equal distribution within each class. This well help us when it comes to comparisons across regions. Then there is the choice of class colors and to decide the color gradient. If the shades are too close together, you won’t be able to see a significant difference across the map, but if they are radically different, we wont get a sense of increasing intensity. Finally, another issue to consider is that larger areas on the map may distort the overall picture or story we are getting because they take up more visual space, this doesn’t necessarily correspond to the actual statistical number they represent.
To solve the problem of areas distorting representation, we have the proportional map, where the physical count of each statistic dictates the size of the area it is representing. In this proportional map of the electoral votes in the US, the designer has designated one square to represent each electoral vote in each state. This affects the perspective of the election in a very significant way. Mow when we look at the original map of the New York Times, it looks significantly red, and seems like an overwhelming majority voted for Bush. With the proportional map, you can now see much more blue and its obvious that the election was much closer than represented.