Predominant Populations in the US

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Why We Love It

This map tells the story of predominant race or ethnicity in the United States the way people experience it: neighborhood by neighborhood. We can clearly see areas where one race or ethnicity is predominant—revealing striking patterns in many cities. We love how quickly we can see areas where the majority of people are of one race or ethnicity, and areas where the population is more evenly balanced.

Why It Works

This map uses bright colors to identify the predominant racial or ethnic group in each area. The strength of the color indicates how high the population of one group is compared to the next most populous. The map is multiscale, meaning it shows specific things at specific scales. When you zoom out you can see how patterns change when data becomes less granular.

Important Steps

Take any dataset that has multiple columns of data, each with a count of related things. For example, use counts of households by income level or use counts of people by education level.

Add a text field to calculate which column has the highest value and write that column’s alias to that text field. The sum of the columns is the total count for this group of fields.

Add a numeric field to calculate the gap between the largest value and the next largest value, as a percent of total.

Use a unique value renderer on the text field, and vary each feature’s transparency based on the percent gap field.

Requirements

Data

Predominance maps are possible when you have two or more columns of count or percent data, and you want to know which is predominant and by how much.

Analysis

Predominance is determined by evaluating two or more columns of similar counts. The highest count wins. The degree of predominance is based on the difference between the largest and the next largest relative to the total of all counts.

Time

In ArcMap it will take four hours by hand or one hour with ModelBuilder. In ArcGIS Online, a map like this can be created from a feature layer in five minutes. See this blog for details.

Tip

Transparency helps visually communicate which areas are predominantly one thing or another, and which have a slim majority.

More Information

Map Author

Andrew Skinner

Andrew Skinner

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Long-time cartographer and map designer in print and online, specializing in the effective use of color, working on basemaps, story maps and anything else you care to throw at me.

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