Area-weighted redistribution between polygon layers

Usage

redistribute_direct(
  source,
  target,
  extensive = NULL,
  intensive = NULL,
  preserve_totals = TRUE,
  suffix = NULL
)

Arguments

source: An sf polygon layer carrying the values to redistribute.
target: An sf polygon layer to estimate values for.
extensive: Character vector of count column names in source to redistribute as totals (area-share weighted, optionally rescaled to preserve the source total).
intensive: Character vector of rate/density column names in source to redistribute as area-weighted means.
preserve_totals: Logical; if TRUE (default) extensive results are rescaled so each target column sums to the source total.
suffix: Optional string appended to each new column name.

Value

The target layer (an sf object) with one new column per redistributed measure.

Details

Extensive measures (counts) are redistributed by each intersection's share of the source polygon area and, when preserve_totals = TRUE, rescaled so the target totals match the source totals. Intensive measures (rates/densities) are area-weighted means: the sum of each source value times the intersection's share of the target polygon area (the standard areal-weighting intensive estimator). This equals a true area-weighted mean when the target is fully covered by the source and treats any uncovered part of a target as contributing zero. NA source values are omitted from the weighted sums. Targets that no source polygon covers receive 0 for extensive measures and NA for intensive measures. If target already has a column named like a redistributed measure, it is overwritten; pass suffix to keep both.

Examples

src <- sf::st_sf(pop = 100, geometry = sf::st_sfc(
  sf::st_polygon(list(rbind(c(0,0), c(2,0), c(2,2), c(0,2), c(0,0)))),
  crs = 3857))
tgt <- sf::st_sf(id = c("A", "B"), geometry = sf::st_sfc(
  sf::st_polygon(list(rbind(c(0,0), c(1,0), c(1,2), c(0,2), c(0,0)))),
  sf::st_polygon(list(rbind(c(1,0), c(2,0), c(2,2), c(1,2), c(1,0)))),
  crs = 3857))
redistribute_direct(src, tgt, extensive = "pop")
#> Simple feature collection with 2 features and 2 fields
#> Geometry type: POLYGON
#> Dimension:     XY
#> Bounding box:  xmin: 0 ymin: 0 xmax: 2 ymax: 2
#> Projected CRS: WGS 84 / Pseudo-Mercator
#>   id                       geometry pop
#> 1  A POLYGON ((0 0, 1 0, 1 2, 0 ...  50
#> 2  B POLYGON ((1 0, 2 0, 2 2, 1 ...  50