This vignette introduces some of the most common measures of
administrative splits. These functions are designed around common
concerns generalized to keeping together “political subdivisions”. See
the vignette “Using redistmetrics” for the bare-bones of
the package.
We first load the redistmetrics package and data from
New Hampshire. For any function, the shp argument can be
swapped out for your data, county for your administrative
unit, and the plans argument can be swapped out for your
redistricting plans (be it a single plan, a matrix of plans, or a
redist_plans object).
library(redistmetrics)
data(nh)The most typical thing to check in a redistricting plan is how many counties are split by a plan. The units need not be counties, but are typically some form of administrative unit. (This is often of interest because, theoretically, each redistricting plan need only split one less county than it has districts.)
Every unit needs to be assigned to an administrative unit.
The number of administrative splits can be computed with:
splits_admin(plans = nh$r_2020, shp = nh, admin = county)
#> [1] 6 6Secondarily, we are often interested in how many municipalities are
split by a plan. These units are smaller and may not cover the entire
state. Units which are not assigned to a sub-administrative unit should
be assigned NA.
The number of sub-administrative splits can be computed with:
splits_sub_admin(plans = nh$r_2020, shp = nh, sub_admin = county)
#> [1] 6 6(Often you would not check county here, but instead some
unit smaller than a county.)
Beyond knowing how many administrative units are split, we may want to know how many are split more than once. We define splitting a unit more than once as a “multi-split”.
Every unit needs to be assigned to an administrative unit.
The number of multi-splits can be computed with:
splits_multi(plans = nh$r_2020, shp = nh, admin = county)
#> [1] 0 0Finally, if a state has a special condition, you may be interested in how many times a particular administrative unit is split. We count here the number of districts that appear within an administrative unit. Unlike most other functions, this returns a matrix, where rows are counties and columns are plans.
The number of splits for each county can be computed with:
splits_count(plans = nh$r_2020, shp = nh, admin = county)
#> [,1]
#> Belknap County 1
#> Carroll County 2
#> Cheshire County 1
#> Coos County 1
#> Grafton County 2
#> Hillsborough County 2
#> Merrimack County 2
#> Rockingham County 2
#> Strafford County 2
#> Sullivan County 1