Population of the regions that contain a unit, and of those that do not

Summarises where a set of point-located units sits relative to the regions of a statistical geography: how many regions hold at least one unit, and what share of the population lives in them.

Usage

region_coverage(region, population, units)

Arguments

region: Region identifiers, one per region, not repeated.
population: Population of each region, same length and order.
units: Number of units located in each region. Zero is the expected value for most regions in most geographies.

Value

A data frame of class rmbl_region_coverage, one row per region, with the columns region, population, units, has_unit and pop_share, ordered by units then population. The totals are carried on the coverage attribute and printed by the print method.

Details

The share this returns is CONTEXT, not a denominator, and the distinction is the reason the function exists rather than a bare tapply().

A region holding no unit is not an unserved population. Units serve catchments, and a catchment is an administrative fact about where people are sent from; a point location does not state it and cannot imply it. Some geographies were never meant to have one unit each.

So a rate built by summing the populations of unit-holding regions pairs a denominator covering part of the territory with a numerator drawn from all of it. Every such rate is inflated, and inflated unevenly: a dense region holding one unit and a sparse region holding seven distort it in opposite directions. Where numerator and denominator must cover the same population, the defensible figure is the whole-territory one.

The print method says this each time, because the covered share is precisely the number a reader is tempted to divide by.

Examples

# Four regions, two of which hold a facility.
cov <- region_coverage(region = c("A", "B", "C", "D"),
                       population = c(1200000, 800000, 450000, 90000),
                       units = c(3, 0, 1, 0))
cov
#> ── 4 units in 2 of 4 regions ───────────────────────────────────── 
#>   those regions hold 1,650,000 of 2,540,000 residents (65.0%)
#>   2 regions hold none; 890,000 residents (35.0%) live there
#> 
#>  region population units has_unit pop_share
#>       A    1200000     3     TRUE 47.244094
#>       C     450000     1     TRUE 17.716535
#>       B     800000     0    FALSE 31.496063
#>       D      90000     0    FALSE  3.543307
#> 
#>   The covered share is context, not a denominator: units serve
#>   catchments, so a rate over these regions alone would take its
#>   numerator from the whole territory and is inflated.
#> ────────────────────────────────────────────────────────────────── 

# The covered share is reported, and is not a rate denominator.
attr(cov, "coverage")$covered_share
#> [1] 64.96063