EJSCREEN: Environmental Justice Screening and Mapping Tool

How to Interpret a Standard Report in EJSCREEN

Block Groups

One key output from EJSCREEN is a standard printed report that describes a selected location. Sometimes the report might focus on a single Census "block group." A block group is an area defined by the Census Bureau that usually has in the range of 600-3,000 people living in it. The US is divided into more than 200,000 block groups.


More typically, though, an EJSCREEN report will cover a "buffer" area, an area on the map that includes everyone who lives within a certain distance of a point, line or polygon. A point might be a factory seeking an emissions permit, for example, and the report could focus on the demographics and environmental conditions within approximately 1 mile of that factory.

In EJSCREEN, buffers can be drawn up to 10 miles around a point, line or polygon. If you have selected a geographic point, the tool will apply a buffer around that point. The buffer ring will aggregate appropriate portions of the intersecting block groups, weighted by population, to create a representative set of data for the entire ring area, honoring variation and dispersion of the population in the block groups within it. For each indicator, the result is a population-weighted average, which equals the block group indicator values averaged over all residents who are estimated to be inside the buffer.

EJSCREEN's report shows:

The first page of EJSCREEN’s report shows the state, regional and national EJ Indexes for the selected area in tabular form and in a bar chart. "Percentiles" are an important part of EJSCREEN. Every indicator in EJSCREEN is put into perspective by showing its associated percentiles.


Percentages or Percentiles?

A percentage is an absolute term. If you received 80% on a test of one hundred questions you had 80 correct answers.

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.

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. 

The second page shows a map of the selected area and the third page shows:

  • 11 environmental indicators
  • Demographic Index
  • six demographic indicators

The report includes the state, regional and national percentiles for each of the environmental and demographic indicators and for the demographic index. The state, regional and national averages for each of the environmental indicators and demographic indicators are also included as a reference point.