catchmentACS: Isochrone-Based Catchment-Area Profiles from American Community Survey Data with Margin-of-Error Propagation

Analyses in education, public health, and service planning often need population characteristics for the area within a fixed drive time of a site, such as the poverty rate around a proposed preschool classroom. We present catchmentACS, an R package that combines drive-time catchment construction, area-weighted aggregation of American Community Survey (ACS) tract data, and propagation of margins of error to derived rates. A single call produces profiles for multiple sites and travel-time thresholds, recording the source and calculation of each output row. We illustrate the workflow with single-site and multi-site examples requiring no Census API key or routing account. Under an explicit working simulation model, the default intervals are conservative, and the number of indistinguishable site comparisons changes little under two correlation scenarios. Among eighteen synthetic catchments ranked by poverty rate, about one in five pairwise comparisons cannot be distinguished at the 90 percent level. The propagated margins of error thus qualify comparisons based on point estimates alone.