Maps and Classification Criteria

As Applied Demographers, we are often asked to produce maps to better present the information we produce. Geographic Information Systems (G.I.S.) are used to transform this information in maps. The most usual method of visualization are choropleth maps. In this maps we present information by graduating the color of the units of analysis.

I was asked to produce maps to present the following information: percentage of the population who are White, percentage of households with no car and low access to stores, percentage of the population who are Hispanics, and WIC redemptions per capita for the counties of Texas, Louisiana, Mississippi, Alabama, Georgia and Florida.

I am presenting the information in using two classification schemes: Natural Breaks and Quantile Breaks. Deciding on a method of classification has implications on the categories where counties are assigned to.

Figure 1 - Maps produced using Natural Breaks

Figure 2 - Maps produced using Quantile Breaks

Results:

The county with the highest proportion of Hispanics was Webb County, TX. The county with the highest level Of WIC per capita for 2009 was Webb County, TX. The county with the highest level of households without a car and low access to a store was Culberson County, TX and the one with the lowest level were Reagan County, King County, Loving County and Cottle County.

In terms of the clustering it appears that Whites cluster in the Gulf Coast in the states of Florida, Mississippi, and Louisiana. At some degree the whites the counties with highest percent of whites are also in the northeast and north area of Texas and the east coast of Florida. As for Hispanics the counties with highest proportions of this population appear to cluster near the Mexico Border and West Texas; at less concentration some counties in Central and South Florida have a certain degree of clustering. Using the quantile classification methodology the concentration or clustering of Hispanics is in all Texas and South and Central Florida.

Clustering of WIC redemptions per capita, 2008 the counties appear to cluster in Louisiana, the border counties with Mexico and Texas, Central Alabama and Central Florida. Lastly, the clustering of percentage of Households with no car and low access to stores for 2010, the counties with the highest proportions appear to cluster in all Louisiana, Mississippi, West Alabama and North Florida.

Sources:

American Community Survey 2006-2010.

ESRI Maps.