Package: catchmentACS 0.6.0

catchmentACS: Isochrone-Based Area-Weighted ACS Aggregation

Computes American Community Survey (ACS) estimates for the area within a given drive time of each of a set of points, such as the locations of pre-kindergarten classrooms. Such an area is called an isochrone. The drive-time areas come from a routing service, either the 'Open Source Routing Machine' ('OSRM', <https://project-osrm.org/>) or 'openrouteservice' (<https://openrouteservice.org/>), and the ACS 5-year estimates of census tracts come from the Census Bureau (<https://www.census.gov/data/developers.html>) through the 'tidycensus' package, one state at a time. The tracts that overlap an area are combined by area weighting, which uses two weights: the share of each tract's area that lies inside, for counts and rates, and each tract's share of the overlapping area, for the medians and per-person values of three ACS tables (median household income, median home value, and per capita income). A median or per-person value from any other table is added up like a count. Counts, medians, per-person values, and five rates are returned with a margin of error at a chosen confidence level, 90 percent by default, and with a record of the settings, inputs, and package versions behind the run. The five rates are the poverty rate, the shares of households receiving Supplemental Nutrition Assistance Program (SNAP) benefits and Supplemental Security Income, the unemployment rate, and the labor force participation rate. The margins of error of counts and rates use the approximation formulas in chapter 8 of U.S. Census Bureau (2020) "Understanding and Using American Community Survey Data: What All Data Users Need to Know" <https://www.census.gov/programs-surveys/acs/library/handbooks/general.html>. For a count the formula for a sum is applied to the weighted tract estimates, with the weights treated as fixed. For a rate the default is the formula for a ratio. Its margin of error is at least as wide as that of the formula for a proportion, which the handbook gives for ratios whose numerator is part of the denominator, as it is in all five rates. The margins of error of medians and per-person values are an approximation made by the package.

Authors:JoonHo Lee [aut, cre, cph]