Identify Cores of a District (Heuristic)

Creates a grouping ID to unite geographies and perform analysis on a smaller set of precincts. It identifies all precincts more than boundary edges of a district district boundary. Each contiguous group of precincts more than boundary steps away from another district gets it own group. Some districts may have multiple, disconnected components that make up the core, but each of these is assigned a separate grouping id so that a call to sf::st_union() would produce only connected pieces.

Usage

make_cores(.data = cur_map(), boundary = 1, focus = NULL)

redist.identify.cores(adj, plan, boundary = 1, focus = NULL, simplify = TRUE)

Arguments

.data: a redist_map object
boundary: Number of steps to check for. Defaults to 1.
focus: Optional. Integer. A single district to focus on.
adj: zero indexed adjacency list.
plan: An integer vector or matrix column of district assignments.
simplify: Optional. Logical. Whether to return extra information or just grouping ID.

Value

integer vector (if simplify is false). Otherwise it returns a tibble with the grouping variable as group_id and additional information on connected components.

Details

This is a loose interpretation of the NCSL's summary of redistricting criteria to preserve the cores of prior districts. Using the adjacency graph for a given plan, it will locate the precincts on the boundary of the district, within boundary steps of the edge. Each of these is given their own group. Each remaining entry that is not near the boundary of the district is given an id that can be used to group the remainder of the district by connected component. This portion is deemed the core of the district.

Examples

data(fl250)
fl250_map <- redist_map(fl250, ndists = 4, pop_tol = 0.01)
#> Projecting to CRS 3857
plan <- as.matrix(redist_smc(fl250_map, 20, silent = TRUE))
core <- redist.identify.cores(adj = fl250_map$adj, plan = plan)
redist.plot.cores(shp = fl250, plan = plan, core = core)