Changes to Census Tract boundaries: 1990-2000	No. 8 May 2003

The Delaware Valley Regional Planning Commission (DVRPC) is an interstate, inter-county, and intercity agency serving the Philadelphia-Camden-Trenton Metropolitan area. As the region's metropolitan planning organization (MPO), the commission provides technical assistance and services to its member state, county and local governments, the private sector and the public. The DVRPC region includes five Pennsylvania counties (Bucks, Chester, Delaware, Montgomery and Philadelphia) and four New Jersey counties (Burlington, Camden, Gloucester and Mercer). Delaware Valley Data is our periodic series of free reference guides, data bulletins and analytical reports. This data reference guide describes changes to census tract boundaries that were made by the United States Census Bureau between the 1990 and 2000 census.

Background

Census tracts are small, statistical subdivisions of a county delineated by local participants as part of the United States Census Bureau's Participant Statistical Areas Program. The primary purpose of census tracts is to provide a stable set of geographic units for the presentation of decennial census data. The 2000 census marks the first time that the entire United States is delineated into census tracts.

Census tracts are identified by a four-digit basic number and may have a two-digit numeric suffix; for example, 6059.02. The Federal Information Processing Standards (FIPS) code for each tract also includes a two-digit state prefix followed by a three-digit county code ( for example, FIPS code "42017 1001.01" identifies a tract located in Bucks County (017), Pennsylvania (42)). The decimal point separating the four-digit basic tract number from the two-digit suffix is shown in printed reports and on DVRPC maps. In computer-readable files, the decimal point is implied.

Generally, between 1,500 and 8,000 people live in a census tract, with an optimum size of 4,000 people. The spatial size of census tracts varies significantly depending on the density of development. When first delineated, census tracts were designed to be homogeneous with respect to population characteristics, economic status, and living conditions. It was also intended that tract boundaries be maintained over several decades so that statistical comparisons could be made from one decennial census to the next. However, physical changes in street patterns caused by highway construction and new development have required occasional boundary revisions. Additionally, census tracts occasionally have been split (due to population growth) or combined (as a result of substantial population decline). Proposed boundaries are reviewed by local, state, or tribal governments, which may adjust them to reflect new visible features and better define the geographic area, or to account for shifts and changes in the population distribution within an area.

If a census tract is split, the two (or more) new tracts are usually assigned unique numbers; tract "42101 347", for example, may be split into two tracts identified as "42101 347.01" and "42101 347.02". Similarly, census tracts which have been created by combining several tracts into one should also be assigned a unique number, as should census tracts whose boundaries are significantly revised from one decennial census to the next. Assigning a unique number to newly-defined tracts prevents researchers from comparing tracts whose boundaries have been significantly revised from one decade to the next.

In numerous cases in the Delaware Valley, however, combinations of two or more 1990 census tracts were assigned one of the 1990 tract numbers (usually of the largest tract) as the new 2000 tract number. In some cases, small "slivers" of land that had been split from the original tract in a previous census (usually labelled with ".98" or ".99" suffixes) were added back on to adjacent larger tracts. In other cases, tracts with declining populations were combined with adjacent tracts. Table 1 lists tract combinations that were assigned a number identical to one of the original 1990 tract numbers by the United States Census Bureau. Historical analysis of population trends in any of these tracts should be done with caution, since in some cases there may be a 1990 tract with a number identical to that of a 2000 tract which in reality has very different geographic boundaries.

Census Tract Changes in the Delaware Valley

Numerous census tract boundaries in the Delaware Valley were revised between 1990 and 2000. The re-drawing of census tract boundaries (as opposed to combining or splitting tracts) usually occurs as the result of physical changes in visible features (including street patterns), political redistricting, or legal challenges. These changes, shown in purple on the attached county maps, can occur almost anywhere and are consequently scattered somewhat randomly across the region. The following discussion instead focuses on tracts that were split or consolidated due to population growth or decline.

Delaware, Chester and Philadelphia counties had relatively few tract changes. In Delaware County, the only census tract that was split is located in Upper Darby Township, while several tracts, concentrated mainly in and around the city of Chester, were consolidated. Chester County had few tract combinations and only four splits (in Uwchlan, West Whiteland, East Goshen and Pocopson Townships). Although Philadelphia County experienced very few splits among its many census tracts, some splits did occur in West and South Philadelphia and, most notably, in the far Northeast.

The majority of the tract splits in DVRPC's Pennsylvania counties occurred in Montgomery and Bucks counties. In Montgomery County, census tract splits were dispersed throughout the county, while in Bucks County, tract splits occurred primarily in the southern portion of the County, between the boundaries of Northeast Philadelphia and Trenton, New Jersey.

A greater number of census tract boundaries were revised across the Delaware River in DVRPC's four New Jersey counties (Mercer, Burlington, Camden and Gloucester) than in the region's Pennsylvania counties. In Mercer County, numerous tracts were split around the Trenton metropolitan area, as well as in East Windsor and West Windsor townships. Parts of Burlington County experienced significant growth since the 1990 census, resulting in census tract splits in Evesham and Mount Laurel townships. Several census tracts were split in Camden County, most notably in the County's faster-growing southeastern municipalities. Gloucester County had the fewest revisions to tract boundaries, with no consolidations and only one split (in Washington Township).

Appendix A lists census tract splits and combinations, while Appendix B identifies census tracts where boundaries have changed. The attached maps (one for each of the region's nine counties) illustrate 2000 census tract boundaries, highlighting tracts which were split, consolidated or otherwise revised.

While every effort has been made to review and clearly display all the changes, some revisions may be subtle and/or confusing. The reader is therefore advised to consult the United States Census Bureau's web site for further information if a detailed analysis is being undertaken that involves any of the census tracts listed in the appendices. Historical comparisons of data for any tracts that have been split or combined with other tracts since 1990 should be done with caution.

Source: Delaware Valley Regional Planning Commission, April 2003. Any historical comparisons of demographic trends in these census tracts should be undertaken with caution.

Notes: No census tracts were combined between 1990 and 2000 in Gloucester County, New Jersey.
** Parts of each of five separate tracts in Chester County were combined to form two new tracts, one of which retained the same number as one of the 1990 tracts despite having a different geography (42029 3001.08). In addition to this tract combination, one census tract in Chester County (42029 3036) was split into two separate tracts (42029 3036 and 42029 3109), one of which has the same number as the original 1990 tract (42029 3036).

Data reference guide #8 is the eighth in a series of guides designed to complement our traditional data releases by explaining specific data sources and methodologies. For more information on Data Reference Guides as well as Analytical Reports and traditional Data Bulletins, please visit the Delaware Valley Regional Planning Commission's website (www.dvrpc.org) or contact DVRPC at the telephone number below.

The Delaware Valley Regional Planning Commission was established in 1965 by interstate compact between Pennsylvania and New Jersey to plan for the orderly growth and development of the region, and to provide a variety of planning and technical assistance services responding to regional issues. DVRPC maintains a significant database for twenty-eight counties encompassing New Jersey, Delaware, Pennsylvania and Maryland. Included in the database are data profiles at the regional, county and municipal level and for other census geography as requested. DVRPC produces a diverse range of services, including demographic and economic data and projections; mapping and aerial photography; computer assisted mapping; geographic information systems; impact studies; and policy and program development.

Appendix A
Appendix B
County Maps: Bucks | Burlington | Camden | Chester | Delaware | Gloucester | Mercer | Montgomery | Philadelphia

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