The Neighborhood Change Database is based on the geographic unit of the Census
Tract. The Census Tract is the Census Bureau's statistical equivalent of a large
neighborhood (with an average of about 4,000 people).
You can select any of the 6 geographical levels:
- Nation (United States)
- States (50 + District of Columbia)
- Counties (3,141)
- Tracts (depends upon the census 35-73,057)
- CBSA – Core Based Statistical Areas
- CSA – Combined Statistical Areas
The data will be presented at the tract level only, but each record has
for larger geographies (such as county, metropolitan areas, places) so it
is possible for you to summarize the tracts in other database or statistical
programs.The geographic identifiers that are included in NCDB for 2010 tract boundaries are: State, Region, Division, County, County Subdivision, Place, American Indian Area/Alaska Native Area/Hawaiian Home Lands, American Indian Tribal Subdivision, Alaska Native Regional Corporation, Metropolitan Statistical Area/Micropolitan Statistical Area, Metropolitan Division, Combined Statistical Area, New England City and Town Area, Combined New England City and Town Area, Congressional District, State Legislative District (Upper Chamber), State Legislative District (Lower Chamber, Voting District, Zip Code Tabulation Area, School District (Elementary), School District,(Secondary), School District (Unified).
The 1970 and 1980 censuses did not have full tract coverage of the US. The
tracts are predominantly located in urban areas. By 1990 the US was fully
tracted and all parts of the country were covered.
The actual remapping procedure for converting data from 1970, 1980, 1990, 2000 tracts to 2010 tract boundaries is quite complicated. Those wishing more a technical explanation of this task should consult Appendix J of the
Data Users' Guide.
The basic procedure was to use geographic information system (GIS) software to overlay the boundaries of 2000 tracts with those of an earlier year. This allowed us to identify how tract boundaries had changed between censuses. We then used 2000 block data to determine the proportion of persons in each earlier tract that went into making up the new 2010 tract. For example, if a 2000 tract split into two tracts for 2010, the population may not have been divided evenly. Our method allows us to determine the exact weight to allocate to each portion.
These population weights were then applied to the various 1970, 1980, 1990, and 2000 tract level NCDB variables to convert them to 2010 tract boundaries. The population weights were used to convert all variables based on counts of persons, households, and housing units, all counts based on subpopulations (such as black persons or elderly households), and all aggregate data (such as aggregate household income). Proportions (such as the proportion of Hispanic persons) were remapped by first converting the respective numerator and denominator values (Hispanic persons and total persons, respectively) and then recalculating the proportion.