For Presentation at the
ESRI International User Conference
July 12th, 2011
This presentation was created by the Census Bureau for the 2011 ESRI International User Conference, a technical audience of Geographic Information Systems (GIS) users. FHWA has modified it and added notes to make the presentation more accessible to a general transportation planning audience. Urban Areas for the 2010 Census
After every decennial Census, the Census Bureau reviews and revises the criteria they use to define urban areas. Incorporated places may have very extensive boundaries that incorporate both rural and urban land, and some unincorporated areas may have development patterns with high population densities. Thus, the traditional method of using place boundaries (incorporated place or census designated place) as the basis for defining urban areas resulted in inconsistencies that were less than ideal. For the Census 2000, the Census Bureau took advantage of increased functionality of Geographic Information Systems (GIS), allowing for more consistent delineation processes. For the 2010 Census, the Census Bureau built upon this foundation to continue its efforts to produce an objective, comparable, and consistent urban area delineation.
Today's criteria applied to 2010 Census results use population counts, population density, and non-residential developments that are part of the urban landscape (e.g. industrial areas).
For the 2010 Census urban/rural delineation, the Census Bureau used ArcGIS 9.x software, employing Visual Basic for Applications (VBA) script and using ArcObjects to automate the delineation process for each major step:
The incorporation of impervious surfaces into the criteria is new, and is meant to include commercial and industrial areas with low population density that are functionally part of the urban area, instead of relying only on residential densities to define urban areas. For this, the 2001 National Land Cover Database (NLCD), or NLCD 2006 update where available, impervious 30 meter raster dataset was used.
ArcGIS Spatial Analyst was used to identify the impervious qualifying Blocks, employing the following procedure:
An animation demonstrates the GIS software performing the initial delineation process for an example geographic area that contains several urban areas.
The Census Bureau includes territory that is not contiguous with the urban core through "hops" and "jump" to allow for the inclusion of densely settled areas proximate to the urban core. Hops must connect along a road segment less than 0.5 miles in length (excluding exempted territory). Jumps can connect along a road segment up to 2.5 miles in length (excluding exempted territory). The 2010 Census criteria does not allow hops after a jump.
Areas qualify for inclusion via a hop or a jump if the area's total population is greater than 1,000 persons or if the population density of the area and the hop/jump corridor is greater than 500 ppsm.
Once hops and jumps have been identified, Census Blocks adjacent to the connecting roadway are evaluated for population density. The hop or jump territory and the highest-density adjacent census blocks are included in the urban area if the total population of the destination is greater than 1,000 residents, or if the population density of the destination and the hop/jump corridor is greater than 500 persons per square mile.
***same image as previous slide but with the addition of the black-highlighted blocks.
Enclaves are small areas of non-qualifying territory that are surrounded by qualifying land and/or non-qualifying water territory. There are three types of enclaves:
Less than or equal to 5 square miles,surrounded by qualifying land only
Less than or equal to 5 square miles, surrounded by qualifying land and non-qualifying water territory
Following the inclusion of enclaves, indentations within the preliminary urbanized area shape are evaluated for inclusion in the final urbanized area. Indentations are areas of non-qualifying territory that are not completely surrounded by qualifying land and/or non-qualifying water (as enclaves are), but are substantially surrounded by qualifying land (according to the Census Bureau criteria).
Many small areas will be identified for potential inclusion in urban areas that are below the population threshold to qualify as an urban area.
Removal of the non-qualifying cores and inclusion of indentations leaves only the high-density, compact areas as qualifying urbanized areas.
You can see by these examples that the edges can still be quite jagged. For the Census Bureau's purposes this is not important, but this is one reason why FHWA allows States/MPOs to create "Adjusted Urbanized Areas," adding additional territory to smooth out jagged edges.
Vincent Osier, Kevin Hawley, Chris Henrie, Ted Sickley
Geographic Standards and Criteria Branch
U.S. Census Bureau