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Geographic boundaries of U.S. Postal Service five-digit ZIP Code areas from HERE, aligned to the street centerlines of the Q2 2018 HERE core map release.
HERE (the company that now includes data products that were formerly branded as "Navteq") maintains several versions of postal code data. The version distributed by MassGIS is an extract of HERE's nationwide "Un-generalized, High Definition, with County" layer. Relative to HERE's standard Postal Code Boundaries product, a significant amount of line work was created for this HD version to better segregate delivery to adjacent ZIP codes. The HERE Map line work was still used as much as possible. Boundaries have increased detail to more closely reflect postal code delivery. In this HD version, multi-part ZIP Code boundaries are allowed more often, when needed to reflect non-contiguous postal delivery. This dataset displays water features on coastlines but does not include "holes" for inland water bodies, and includes ZIP Code boundaries split at County boundaries.
The HERE Postal Code Boundaries product does not have void areas in postal coverage, even if such non-delivery areas exist in reality (such as a remote mountainous area). This is by design, for aesthetic purposes and to ensure that a postal code is assigned to all geographic areas.
MassGIS made minor edits to a few ZIP Code boundaries in Boston based on address data from the city. MassGIS also projected the data into the Massachusetts State Plane Mainland coordinate system.
2020 Census tracts are small, relatively permanent statistical subdivisions of a county or equivalent entity, and are reviewed and updated by local participants prior to each decennial census as part of the Census Bureau’s Participant Statistical Areas Program (PSAP). The primary purpose of census tracts is to provide a stable set of geographic units for the presentation of decennial census data.Census tracts generally have a total population size between 1,200 and 8,000 people with an optimum size of 4,000 people. The spatial size of census tracts varies widely depending on the density of settlement. Ideally, census tract boundaries remain stable over time to facilitate statistical comparisons from census to census. However, physical changes in street patterns caused by highway construction, new development, and so forth, may require boundary revisions. In addition, significant changes in population may result in splitting or combining census tracts. State and county boundaries always are census tract boundaries in the standard census geographic hierarchy, but tracts can cross the same kinds of boundaries that block groups can. Census tract numbers have up to a 4-character basic number and may have an optional 2-character suffix. The census tract numbers (used as names) eliminate any leading zeroes and append a suffix only if required. The 6-digit census tract codes, however, include leading zeroes and have an implied decimal point for the suffix. Census tract codes (000100 to 998999) are unique within a county or equivalent area.