About the Project

Though choropleth mapping and area cartograms are two of the most common techniques for mapping thematic variables such as foreign-born population, each have significant drawbacks. Choropleth maps fail to distinguish between areas of high and low population. Area cartograms address that issue but can be difficult to interpret given the spatial distortions they introduce. Roth et al. (2010) have developed a new method for developing thematic maps: value-by-alpha mapping.  In the case of foreign-born population maps the value-by-alpha technique uses varying opacities to highlight areas of high population density and deemphasizes areas of low population density. This equalizes foreign-born population based on density and show the percentage of population in each county that were born outside the US—all while preserving both shape and topology. Utilizing this method for foreign-born population effectively highlights high density areas with large foreign-born populations, showing patterns that would likely be missed with traditional choropleth or area cartogram mapping techniques.