Figure 5-3 Upper bound estimate of percentage of housing units with no vehicle, Long Island, New York, by block group, 2006–2010

SOURCES: Calculated from 2006–2010 American Community Survey, Table B25044; adapted from workshop presentation by Steven Romalewski.

the Census Bureau issued a special tabulation from 5-year 2006–2010 ACS data for use in legislative redistricting and more easily assessing the equity of newly drawn districts. Known as the Voting Age Population by Citizenship and Race tabulation—or CVAP for short—the file contains counts of voting-age U.S. citizens (and their associated margins of error) for geographic units from the nation as a whole down to the census block group level. The maps Romalewski displayed using CVAP data grew out of work that the Mapping Center has been doing with a group involved with boosting civic engagement among the Long Island population; in particular, this set of maps examined the percentage of the total CVAP population in each tract that is of Hispanic origin. Given this application area, one instinctive “answer” to the problem of volatility in the ACS estimates—switching to a more aggregate level of resolution like county subdivisions or defined villages—is not really viable; higher-level geographic aggregates are far from optimal for purposes of planning specific, targeted voter registration drives or activities affiliated with schools.

Using the CVAP data, Romalewski began by repeating the approach of generating separate maps based on lower-bound and upper-bound estimates for per-

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