Frequent Questions about the Power Plants and Neighboring Communities Mapping Tool
On this page:
- What is the Power Plants and Neighboring Communities Mapping Tool?
- What is the purpose of Power Plants and Neighboring Communities Mapping Tool?
- How do I use the Power Plants and Neighboring Communities Mapping Tool?
- What are the included socioeconomic indicators?
- What are the demographic indexes?
- Why is a three-mile radius around power plants presented as the uniform buffer?
- How is the summary information determined for the buffer around each plant?
- What is a percentile and why is it used?
- Why are areas at or above the 80th percentile sometimes highlighted?
- What are the data sources and what years do the data represent?
- How are power plant emissions determined?
- Is data available for download?
- Are there limitations using the data to assess community impacts?
- How do I cite the Power Plants and Neighboring Communities Mapping Tool?
- How do I provide feedback?
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1) What is the Power Plants and Neighboring Communities Mapping Tool?
Power Plants and Neighboring Communities Mapping Tool is an interactive tool that presents fossil fuel-fired power plant emissions data (e.g., SO2, NOX, CO2) with summaries of the socioeconomic characteristics of the communities near or downwind of those plants.
2) What is the purpose of Power Plants and Neighboring Communities Mapping Tool?
The Power Plants and Neighboring Community Mapping Tool and associated data help identify and characterize the communities that may be exposed to air pollution from power plants. The tool improves access to publicly available data through interactive maps and graphs where users can explore a specific geographic area of interest, such as where they live, or see a comprehensive view of the socioeconomic characteristics of all communities near and downwind of power plants in the United States.
3) How do I use the Power Plants and Neighboring Communities Mapping Tool?
Users can interact directly with the map on the webpage, using GIS layers and filters. The available layers are listed on the right side of the map. A subset of the layers are visible when the map is initially loaded, but many are not visible until the user selects them or the user zooms into a smaller geographic region. Users can turn layers on or off by clicking the “eye” icon to the right of the layer name.
Users can also filter the map results according to different parameters (e.g., power plant fuel, emissions) to provide information about power plant characteristics and community socioeconomic characteristics.
To learn more about navigating online maps, visit the Finding and Navigating Maps in ArcGIS Online website for a short video and interactive sample map.
4) What are the included socioeconomic indicators?
The various socioeconomic indicators displayed in the Power Plants and Neighboring Communities Mapping Tool are from the U.S. Census Bureau and EPA. They include race/ethnicity, income, age, language, and education.
More information is available in this Overview of socioeconomic indicators in EJScreen and associated documentation (e.g., the Technical Documentation for EJSCREEN).
5) What are the demographic indexes?
The demographic index is based on the average of two demographic indicators: low-income population and people of color. See EPA’s definition of low-income population and people of color.
The supplemental demographic index is based on the average of five socioeconomic indicators; low-income, unemployment, limited English, less than high school education, and low life expectancy (which is a health dataset).
More information can be found in the section 2, “Overview of Data in EJScreen”, of the Technical Documentation for EJScreen.
6) Why is a three-mile radius around power plants presented as the uniform buffer?
A three-mile radius is commonly used for proximity analysis. This scale provides useful insights regarding the population living within the immediate vicinity of a pollution source and does not consider factors such as stack height or weather that could affect the areas ultimately exposed to air pollution.
7) How is the summary information determined for the buffer around each plant?
EPA calculates the summary information for the areas around plants (i.e., buffers). The socioeconomic summary for a buffer is designed to represent the average resident within the buffer, and provide an estimate of the total population residing in the buffer. U.S. Census Bureau-defined block groups and blocks are used to determine the summary socioeconomics. Some block groups will be partly inside and partly outside the buffer, and the buffer analysis must estimate how much of each block group’s population is inside the buffer.
The methodology estimates the fraction of the Census block group population that is inside the buffer by using block-level population counts from Census 2020. These blocks provide data at a higher resolution than block groups. Each block has an internal point defined by the U.S. Census Bureau, and the entire block population is counted as inside or outside the buffer depending on whether the block internal point is inside or outside.
The calculation of a value for the buffer is the population-weighted average of the indicator values in the blocks included in the buffer, where each block uses the indicator values of the block group containing it. A block group is weighted based on the fraction of the U.S. Census Bureau’s American Community Survey (ACS) block group population that is considered in the buffer. That fraction is estimated as the Census block population divided by the Census block group population.
Detailed information about calculating data for surrounding buffers can be found in section 6, “Buffer Reports”, of the Technical Documentation for EJScreen.
8) What is a percentile and why is it used?
Percentiles are a way to see how local residents in a given community compare to everyone else in the United States. Percentiles let you compare a community to the rest of the nation. The national percentile tells you what percent of the U.S. population has an equal or lower value.
For example, if an area is 50% people of color and is at the 70th national percentile, this means that 50% of the area’s population is people of color, and that is an equal or higher percentage of people of color than where 70% of the U.S. population lives.
9) Why are areas at or above the 80th percentile sometimes highlighted?
EPA sometimes uses the 80th percentile as a starting point for the purpose of identifying geographic areas that may warrant further consideration, analysis, or outreach. The Power Plants and Neighboring Communities Mapping Tool enables users to identify communities based on various socioeconomic and environmental factors. Communities above the 80th percentile for any socioeconomic indicators are communities where a particular socioeconomic indicator is at a level equal or higher than where 80% of the U.S. population lives (i.e., 80th percentile nationally).
10) What are the data sources and what years do the data represent?
The data is updated annually to the latest available. The following table presents the data source, source website, and the year or version of data currently reflected in the tool.
| Data Type | Data Source | Data Year or Version |
|---|---|---|
| Emissions | Emissions & Generation Resource Integrated Database (eGRID) | US EPA | 2022 |
| Emissions | Clean Air Power Sector Programs | US EPA | 2023 |
| Socioeconomic Information | EJScreen: Environmental Justice Screening and Mapping Tool | US EPA | Census Bureau’s ACS 2018-2022 5-year Summary accessed via EJScreen Version 2.3 |
| Downwind Areas | EPA's Power Plant Proximity and Downwind Analysis | 2022 |
The Power Plants and Neighboring Communities Mapping Tool webpage and the Announced Power Plant Retirement map pages provide additional details on data years and data sources.
11) How are power plant emissions determined?
For a subset of power plants (generally, those that are above 25 MW nameplate capacity), the SO2, NOX, and CO2 emissions are directly reported to EPA and published in CAPD’s Power Sector Emissions data. PM2.5 data is reported under EPA’s National Emissions Inventory (NEI).
12) Is data available for download?
Yes, data is available for download from the Power Plants and Neighboring Communities Mapping Tool webpage.
13) Are there limitations using the data to assess community impacts?
The Power Plants and Neighboring Communities Mapping Tool only presents power plant information and helps identify and characterize the communities that may be exposed to air pollution from those plants.
The Power Plants and Neighboring Communities Mapping Tool does not, however, evaluate air quality impacts or quantify the potential health risk to those populations.
14) How do I cite Power Plants and Neighboring Communities?
The following citation for Power Plants and Neighboring Communities Mapping Tool is suggested:
United States Environmental Protection Agency (EPA). 2025. “Power Plants and Neighboring Communities Mapping Tool (PPNC), 2025” Washington, DC: Office of Atmospheric Protection, Clean Air and Power Division. Available from EPA’s Power Plants and Neighboring Communities web site.
15) How do I provide feedback?
We appreciate feedback! Please use this form.
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