Relating Block Groups to ZIP Code Areas

.. the popularity of block group demographic data is mainly due to this being the smallest geographic area for which annually updated demographic data, with U.S. wall-to-wall coverage, are available from the American Community Survey (ACS) — or any other source. While block groups nest within census tracts from both a geometric and geocode hierarchy perspective, the relationship between block groups and ZIP code areas is far less clear. Analysts are often interested in relating block group geography and demographics with ZIP code areas. The Census 2010 217,740 block groups intersect with 32,824 ZIP code areas forming 308,805 BG-ZIP area combinations. This section reviews tools to examine the relationship between block group geography/demographics and ZIP code areas. See related Web section for full details.

Block Group 06-075-015700-1 in Context of ZIP Code Area 94115
Block groups (BGs) are often wholly contained within a ZIP code area. But around the ZIP code area boundary, intersecting block groups are often split by the ZIP code boundary. This relationship is illustrated in the graphic shown below. This graphic shows block group 06-075-015700-1 (yellow BG code label, cross-hatched, black boundary) in context of ZIP Code area 94115 (white labels, bold blue boundary) located in San Francisco. This GIS application is closely related to theĀ Mapping Block Group Data, also uses the San Francisco area in applications.

– view developed with ProximityOne CV XE GIS and related GIS project.
– view all San Francisco ZIP code areas; see ZIP 94115 in context.

The cross-hatched BG 060750157001 (or 06-075-015700-1) is split by ZIP code 94115. What part of the BG is in ZIP code area 94115 and adjacent ZIP code area 94118? The situation is similar for BG 060750157002, directly below 060750157001, which is split into 3 ZIP code areas. Use the interactive table to make these determinations.

Using the Interactive Table
The interactive table illustrated in the graphic below contains a row for block group area part which intersects with a unique ZIP code area. The simple case of a BG being split into two ZIP code areas can be visually observed as shown in the graphic presented above. A tabular relational table offers processing advantages compared to visual geospatial depictions. Here is an example. ZIP code area 94115 contains whole or parts of 32 BGs. To view/verify this using the table below, 1) click the ShowAll button below the table, then 2) click the Find ZIP button (edit box at right preloaded with this ZIP). The table refreshes with 32 rows — the BGs intersecting with this ZIP code area. Verify there are 32 BGs; the BG codes can be viewed in column 1.

In the above map at the top of this section, block group 06-075-015700-1 is shown visually to be contained in two ZIP code areas. To view how block group 06-075-015700-1 is split among multiple ZIP code areas using the table below, 1) click the ShowAll button below the table, then 2) click the Find GEOID button (enter G0607501057001 in the edit box to right of Find GEOID then click Find button). The table refreshes with two BGs. In this example, it can be seen that the total BG population (Census 2010) is 1,375. The part of the BG population is shown and the percent of the population from that BG allocated to the corresponding ZIP code are shown. This BG has a total area 0.09 square miles. The part of the BG area Census 2010, square miles) is shown and the percent of the area from that BG allocated to the corresponding ZIP code are shown.

Use the main Web section interactive table to examine areas of interest. Join me in a Data Analytics Lab session to discuss use of these data using analytical tools and methods applied to your situation.

About the Author
— Warren Glimpse is former senior Census Bureau statistician responsible for innovative data access and use operations. He is also the former associate director of the U.S. Office of Federal Statistical Policy and Standards for data access and use. He has more than 20 years of experience in the private sector developing data resources and tools for integration and analysis of geographic, demographic, economic and business data. Contact Warren. Join Warren on LinkedIn.

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