Racial Dot Maps Based on Dasymetrically Modeled Gridded Population Data

Abstract

Racial geography, mapping spatial distributions of different racial groups, is of keen interest in a multiracial society like the United States. A racial dot map is a method of visualizing racial geography, which depicts spatial distribution, population density, and racial mix in a single, easy-to-understand map. Because of the richness of information it carries, the dot map is an excellent tool for visual analysis of racial distribution. Presently-used racial dot maps are based on the Census data at the tract or the block level. In this paper, we present a method of constructing a more spatially-accurate racial dot map based on a sub-block-resolution population grid. The utility of our dot maps is further enhanced by placing dots on the map in random order regardless of the race they represent in order to achieve a more accurate depiction of local racial composition. We present a series of comparisons between dot maps based on tract, block, and grid data. The advantage of a grid-based dot map is evident from the visual comparison of all maps with an actual image of the mapped area. We make available the R code for constructing grid-based dot maps. We also make available 2010 grid-based racial dot maps for all counties in the conterminous United States.

Racial disparities, environmental exposures, and SARS-CoV-2 infection rates: A racial map study in the USA

“…The racial dot map of non-Hispanic whites and non-Hispanic blacks was used in this study (Figure 1). The 30m grids have been developed using dasymetric modeling, which has a high accuracy of gridded population data over commonly used Census tract/blocks-aggregated data (Dmowska & Stepinski, 2019;Dmowska et al, 2017).…”

A Comparative Study of Methods for the Visualization of Probability Distributions of Geographical Data

“…These traditional techniques consist of placing symbols on a map to represent the spatial distribution of discrete geographic data [38]. A popular application of this map type is the Racial Dot Maps [39], which show the ethnic distribution in discrete geographical regions. The dots are colored according to the corresponding category (race) and are randomly placed inside each region in a way that the proportion of dots of a particular color within a region corresponds to the proportion of the race in that region.…”

Temporal transitions of demographic dot maps

“…Dot maps are also often used to displayed categorical demographic data. Common uses include mapping race or ethnicity (Cable, 2013;Dmowska & Stepinski, 2019), educational attainment (Walker, 2018), or socio-economic status (Barreto, 1993). These maps either present categorical variables in individual maps and then compare them as small multiples (Barreto, 1993), or on the same map via leveraging a qualitative colour scheme (Cable, 2013;Walker, 2018).…”

“…With the advent of interactive web maps, recent research has also focused on how dot maps can be scaled, on-the-fly, to display an appropriate number of dots at different zoom levels (Walker, 2018;Zhang, Zhu, Xiao, & Zhang, 2016). Another strand of recent research is to improve the estimation of dot location via dasymetric mapping, a technique which uses auxiliary data to weight where wthin a zone observations are more likely to occur (Dmowska & Stepinski, 2019;Holt et al, 2004;Petrov, 2012). Auxiliary land use data can be of several forms, such as from a municipality's zoning or land use plans, derived from satellite imagery, or from population counts linked to smaller census boundaries.…”

“…As mentioned in the previous section, there is a wide literature regarding selecting the locations of coordinates of dots on dot maps. These methods vary in sophistication from placing dots at purely random locations within a zone, placing dots in a way where a minimal spacing between dots is achieved, or using a dasymetric mapping technique to place dots in locations based on auxiliary data sources (Dmowska & Stepinski, 2019;Hey & Bill, 2014;Kimerling, 2009;Mackay, 1949). Figure 2 schematically shows different strategies for dot placement.…”