Racial Dot Maps
Last Spring I did a superlecture on the Lockean Proviso of "Enough and as Good" featuring racial dot maps. This is, in some ways, a continuation of that talk.
Texarkana
Dallas
This map is an American snapshot; it provides an accessible visualization of geographic distribution, population density, and racial diversity of the American people in every neighborhood in the entire country. The map displays 308,745,538 dots, one for each person residing in the United States at the location they were counted during the 2010 Census. Each dot is color-coded by the individual's race and ethnicity. The map is presented in both black and white and full color versions. In the color version, each dot is color-coded by race.
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All of the data displayed on the map are from the U.S. Census Bureau's 2010 Summary File 1 dataset made publicly available through the National Historical Geographic Information System. The data is based on the "census block," the smallest area of geography for which data is collected (roughly equivalent to a city block in an urban area).
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The map was created by Dustin Cable, a former demographic researcher at the University of Virginia's Weldon Cooper Center for Public Service. Brandon Martin-Anderson from the MIT Media Lab and Eric Fischer, creator of social media dot maps, deserve credit for the original inspiration for the project. This map builds on his work by adding the Census Bureau's racial data, and by correcting for mapping errors.
Image Copyright, 2013, Weldon Cooper Center for Public Service, Rector and Visitors of the University of Virginia (Dustin A. Cable, creator)
Mini EJSCREEN Walkthrough
6 Demographic Indicatort
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Percent Low-Income
Percent Minority
Less than High School Education
Linguistic isolation
Individuals under 5
Individuals over age 65
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Also two indexes based on above: A Demographic Index based on Percent Low-Income and Percent Minority and A Supplementary Demographic Index based on an average of all six demographic indicators.
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Importantly there is room to play in all of them
Texarkana's Demographic Index Visualized
Minority Population at Equal Interval
Minority Population at Natural Breaks
Minority Population at Quantile
Obviously not all data classification systems visualize the same story.
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As The National Center for Geographic Information and Analysis explains the visualization is only as good as the data behind the visualization and the choices made
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Among the many choices made by analysts and designers, data classification decisions might among the most important, but also the most difficult to understand. A GIS specialist must make choices about not only how many different classes that the data should be categorized into, but what the value ranges of those classes should be. A slight adjustment of the "breaks" in the value ranges of ordered data, for example, might alter the map significantly and reveal trends that were not detected previously (or are not in fact there).
In this section, two of the most common "default" methods of classifying data are presented. These are two of many choices available in recent versions of ArcView, and a designer should be aware of the differences among all of the methods. Each has advantages and disadvantages.
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Quantiles. This method classifies data into a certain number of categories with an equal number of units in each category.
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Equal Intervals. This method sets the value ranges in each category equal in size. The entire range of data values (max - min) is divided equally into however many categories have been chosen
Percentage Black Population
Equal Interval and Natural Breaks
Percentage Hispanic Population
Equal Interval and Natural Breaks
Minority Population
Less Than High School Education
Equal Interval
Minority Population
Lead Paint Indicator
Equal Interval
Household Income
Less than 15K
More than 75K
Pulling Back the Curtain a Bit
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Data Sets from Inside the Loop and Pleasant Grove Areas
Some thoughts on percentages from EJSCREEN
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A percentage is an absolute term. If you received 80% on a test of one hundred questions you had 80 correct answers.
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A percentile is a relative term, and tells you how you have done on the test in comparison to the others who took the test. A percentile of 80 means that you scored equal to or better than 80% of people who took the test.
In EJSCREEN, if your results indicate that an area is 48% minority and is at the 69th national percentile, this means that 48% of the area’s population is minority, and that is an equal or higher % minority than where 69% of the US population lives.
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Percentiles are a way to see how local residents compare to everyone else in the United States. Instead of just showing numbers out of context, EJSCREEN lets you compare a community to the rest of the state, EPA region and nation, by using percentiles. The national percentile tells you what percent of the US population has an equal or lower value, meaning less potential for exposure/ risk/ proximity to certain facilities, or a lower percent minority.
