Environmental Burden Index - Peer Environmental Groups

ATSDR’s Environmental Burden Index (EBI) aggregates multiple environmental data sourced into one easy-to-use index to estimate environmental quality at the Census tract level for the United States.

Other similar tool such as the EPA’s Environmental Quality Index (EQI) estimate environmental quality at the county level, or limit their analysis to a single state as is the case with the CaliEnvroScreen.

The EBI is the first measure of environmental quality to rank national score against ‘like environments’; by comparing environments that are inherently similar the EBI captures environmental quality in a way that no other existing index can.

These ‘like environments’ or Peer Environments Groups are determined by parsing the Census tracts into peer cluster groups based on three factors:

1. The National Land Cover Database (NLCD)

2. U.S Dept. of Agriculture (USDA) Rural-Urban Commuting Area Codes

3. Population Density

We plan to delineate the 74,134 Census tracts using the 16 land cover types, the 10 rural-urban codes, and 3 population density categories (clustered by Jenks natural breaks method into low/medium/high). This makes for a posible 480 tract types, but we anticipate the number of clusters to be much smaller than this as many combinations of categories won’t exist.

1. The National Land Cover Database (NLCD)

The National Land Cover Database (NLCD) serves as the definitive Landsat-based, 30-meter resolution, land cover database for the Nation. National Land Cover Database 2011 (NLCD 2011) is the most recent national land cover product created by the Multi-Resolution Land Characteristics (MRLC) Consortium. As with two previous NLCD land cover products NLCD 2011 keeps the same 16-class land cover classification scheme that has been applied consistently across the United States at a spatial resolution of 30 meters. NLCD 2011 is based primarily on a decision-tree classification of circa 2011 Landsat satellite data. All NLCD data products are available for download at no charge to the public from the MRLC Web site.

A generalized summary of the main NLCD2001 land cover classes for the conterminous United States (Note: Some NLCD2001 land cover classes have been grouped for display purposes.)

2. U.S Dept. of Agriculture (USDA) Rural-Urban Commuting Area Codes

The rural-urban commuting area (RUCA) codes, a detailed and flexible scheme for delineating sub-county components of rural and urban areas, have been updated using data from the 2010 decennial census and the 2006-10 American Community Survey (ACS). RUCA codes are based on the same theoretical concepts used by the Office of Management and Budget (OMB) to define county-level metropolitan and micropolitan areas. We applied similar criteria to measures of population density, urbanization, and daily commuting to identify urban cores and adjacent territory that is economically integrated with those cores. We adopted OMB’s metropolitan and micropolitan terminology to highlight the underlying connectedness between the two classification systems. However, the use of census tracts instead of counties as building blocks for RUCA codes provides a different and more detailed geographic pattern of urban and rural areas.

Census tracts are used because they are the smallest geographic building block for which commuting flow estimates are available from the U.S. Census. Tract-to-tract commuting flow files were constructed from ACS data as part of a special tabulation for the Department of Transportation-the Census Transportation Planning Package. To derive estimates for small geographic units such as census tracts, information collected annually from over 3.5 million housing units was combined across 5 years (2006-10). As with all survey data, ACS estimates are not exact because they are based on a sample. In general, the smaller the estimate, the larger the degree of uncertainty associated with it.

The classification contains 10 primary and 21 secondary codes. Few, if any, research or policy applications need the full set of codes. Rather, the system allows for the selective combination of codes to meet varying definitional needs.

Table 1. Primary RUCA Codes, 2010

1 Metropolitan area core: primary flow within an urbanized area (UA)

2 Metropolitan area high commuting: primary flow 30% or more to a UA

3 Metropolitan area low commuting: primary flow 10% to 30% to a UA

4 Micropolitan area core: primary flow within an Urban Cluster of 10,000 to 49,999 (large UC)

5 Micropolitan high commuting: primary flow 30% or more to a large UC

6 Micropolitan low commuting: primary flow 10% to 30% to a large UC

7 Small town core: primary flow within an Urban Cluster of 2,500 to 9,999 (small UC)

8 Small town high commuting: primary flow 30% or more to a small UC

9 Small town low commuting: primary flow 10% to 30% to a small UC

10 Rural areas: primary flow to a tract outside a UA or UC

99 Not coded: Census tract has zero population and no rural-urban identifier information

3. Population Density

Population density is the number of people per unit of area, usually quoted per square kilometer or square mile. The average population density across the U.S. is 89.5 persons/ sq. mi. New York City has a population density of 27,016 persons/ sq. mi.

For each of the potential 160 Land Cover/ Rural-Urban county groupings that contains at least one county, the group wil be divided into up to 3 sub-groups by performing Jenks natural break grouping method on the population densities. Making for potentially 480 peer environmental groups. Jenks natural breaks optimization is analogous to a one dimensional k-meanscluster analysis.