2) Libraries (minimal)

library(geoDeltaAudit)
library(dplyr)
library(readr)
library(stringr)
library(janitor)

Geographic Data Transformation Audit Workflow

Overview

This workflow measures data perturbation when transforming variables across geographic boundaries. The process reveals two critical decision points typically left implicit in applied work, maintaining variable agnosticism throughout.

Setup and Data Preparation

Step A: Association Construction

## --- load toy baseline (relationship-defined) ---
acs_path <- system.file("extdata", "toy_acs_zcta_hennepin.csv", package = "geoDeltaAudit")
stopifnot(nchar(acs_path) > 0)

acs_zcta_hennepin <- readr::read_csv(acs_path, show_col_types = FALSE) %>%
  janitor::clean_names() %>%
  dplyr::mutate(zcta = stringr::str_pad(as.character(.data$zcta), 5, pad = "0"))

# Toy assoc: 1:1 ZCTA -> ZIP (same 5-digit IDs)
zcta_zip_hennepin <- acs_zcta_hennepin %>%
  dplyr::distinct(.data$zcta) %>%
  dplyr::transmute(zcta = .data$zcta, zip = .data$zcta) %>%
  dplyr::distinct()

assoc_structure <- zcta_zip_hennepin %>%
  dplyr::summarise(
    n_rows  = dplyr::n(),
    n_zctas = dplyr::n_distinct(.data$zcta),
    n_zips  = dplyr::n_distinct(.data$zip)
  )

assoc_structure

## # A tibble: 1 × 3
##   n_rows n_zctas n_zips
##    <int>   <int>  <int>
## 1     74      74     74

Association diagnostics

diagnostics <- audit_association(assoc_table) print(diagnostics)

unmapped <- acs_zcta_hennepin %>%
  dplyr::anti_join(zcta_zip_hennepin %>% dplyr::distinct(.data$zcta), by = "zcta")

fanout_stats <- zcta_zip_hennepin %>%
  dplyr::count(.data$zcta, name = "n_zip") %>%
  dplyr::summarise(
    min    = min(.data$n_zip),
    median = median(.data$n_zip),
    mean   = mean(.data$n_zip),
    max    = max(.data$n_zip)
  )

list(
  n_unmapped_zctas = nrow(unmapped),
  fanout = fanout_stats
)

## $n_unmapped_zctas
## [1] 0
## 
## $fanout
## # A tibble: 1 × 4
##     min median  mean   max
##   <int>  <dbl> <dbl> <int>
## 1     1      1     1     1

Key assumption:

Crosswalks are directional allocations (not inverses) This audit treats each step as a one-way transformation and reports loss/fan-out at each stage

Interpreting Results Tables

Visualizing Perturbations

What this vignette demonstrates

This vignette shows how geoDeltaAudit separates data values from geographic transformation rules.

The maps above visualize how identical source values can yield different spatial memberships depending on whether boundaries are defined by relationships or geometry. The numerical audit steps in other vignettes quantify the downstream effects of these choices.