Merge adjacent grid polygons with given rules

Merge boundary-sharing (in "Rook" contiguity) grids with fewer target features than the threshold. This function strongly assumes that the input is returned from the par_make_grid, which has "CGRIDID" as the unique id field.

Usage

par_merge_grid(
  points_in = NULL,
  grid_in = NULL,
  grid_min_features = NULL,
  merge_max = 4L
)

Arguments

points_in

sf or SpatVector object. Target points of computation.

grid_in

sf or SpatVector object. The grid generated by the internal function par_make_grid.

grid_min_features

integer(1). Threshold to merge adjacent grids.

merge_max

integer(1). Maximum number of grids to merge per merged set. Default is 4. For example, if the number of grids to merge is 20 and merge_max is 10, the function will split the 20 grids into two sets of 10 grids.

Value

A sf or SpatVector object of computation grids.

Note

This function will not work properly if grid_in has more than one million grids.

References

• Polsby DD, Popper FJ. (1991). The Third Criterion: Compactness as a Procedural Safeguard Against Partisan Gerrymandering. Yale Law & Policy Review, 9(2), 301–353.

See also

Other Parallelization: par_cut_coords(), par_grid(), par_hierarchy(), par_make_grid(), par_multirasters(), par_pad_balanced(), par_pad_grid(), par_split_list()

Author

Insang Song

Examples

library(sf)
library(igraph)
#> 
#> Attaching package: ‘igraph’
#> The following objects are masked from ‘package:terra’:
#> 
#>     blocks, compare, union
#> The following objects are masked from ‘package:future’:
#> 
#>     %->%, %<-%
#> The following objects are masked from ‘package:stats’:
#> 
#>     decompose, spectrum
#> The following object is masked from ‘package:base’:
#> 
#>     union
library(dplyr)
#> 
#> Attaching package: ‘dplyr’
#> The following objects are masked from ‘package:igraph’:
#> 
#>     as_data_frame, groups, union
#> The following objects are masked from ‘package:terra’:
#> 
#>     intersect, union
#> The following objects are masked from ‘package:stats’:
#> 
#>     filter, lag
#> The following objects are masked from ‘package:base’:
#> 
#>     intersect, setdiff, setequal, union
library(spatstat.random)
#> Loading required package: spatstat.data
#> Loading required package: spatstat.univar
#> spatstat.univar 3.0-1
#> Loading required package: spatstat.geom
#> spatstat.geom 3.3-2
#> 
#> Attaching package: ‘spatstat.geom’
#> The following objects are masked from ‘package:igraph’:
#> 
#>     diameter, edges, is.connected, vertices
#> The following objects are masked from ‘package:terra’:
#> 
#>     area, delaunay, is.empty, rescale, rotate, shift, where.max,
#>     where.min
#> spatstat.random 3.3-1
options(sf_use_s2 = FALSE)

dg <- sf::st_as_sfc(st_bbox(c(xmin = 0, ymin = 0, xmax = 8e5, ymax = 6e5)))
sf::st_crs(dg) <- 5070
dgs <- sf::st_as_sf(st_make_grid(dg, n = c(20, 15)))
dgs$CGRIDID <- seq(1, nrow(dgs))

dg_sample <- sf::st_sample(dg, kappa = 5e-9, mu = 15,
scale = 15000, type = "Thomas")
sf::st_crs(dg_sample) <- sf::st_crs(dg)
dg_merged <- par_merge_grid(sf::st_as_sf(dg_sample), dgs, 100)
#> ℹ The merged polygons have too complex shapes.
#> Increase threshold or use the original grids.

plot(sf::st_geometry(dg_merged))