split_precinct_analysis {eiExpand}

Split precinct analysis - VAP Adjusted Election Data

Description

Run Split Precinct Analysis using precinct-level geometries and election data, a district shape, and block-level vap data. This function calculates the percent vap of a precinct contained in the district boundary of interest. Then, if specified, multiplies election vote counts by percent vap.

Usage

split_precinct_analysis(
  vtd,
  planShp,
  block_pop_data,
  vote_col_names = NULL,
  lower_thresh = 0.02,
  upper_thresh = 0.98,
  keepOrigElection = TRUE,
  generatePlots = FALSE,
  ggmap_object = NULL,
  verbose = FALSE
)

Arguments

vtd

A sf dataframe with precinct-level geometries potentially in the district from planShp. For election adjustments, it should also contain election results in columns defined in vote_col_names.

planShp

A sf dataframe with one row containing district plan shape boundary (one district).

block_pop_data

A sf object of blocks covering the region, with vap column

vote_col_names

Character vector containing the name of the columns to be adjusted based on percent vap. This should include election results columns names in vtd.

lower_thresh

A decimal. If the percent area of a precinct inside the planShp is equal to or below this threshold, the precinct will be removed. Defaults to .02.

upper_thresh

A decimal. If the percent area of a precinct inside the planShp is equal to or above this threshold, the precinct will be considered to be fully contained in the district. Defaults to .98.

keepOrigElection

A boolean indicating if original election vote counts should be preserved in the output dataset for comparison purposes.

generatePlots

Boolean indicating if function should generate a list of map checking plots. If TRUE, the function output will include a list of plots that show split precincts and intersecting blocks within and outside of the district.

ggmap_object

A ggmap object of the area on interest to be the background of plots if generatePlots = TRUE. If this argument is not specified, plots will be generated without a map background.

verbose

A boolean indicating whether to print out status messages.

Value

If generatePlots = FALSE, returns a split precinct results data.frame with vap percentages and adjusted election data. If generatePlots = TRUE, returns a list with the result data.frame in the first element and the list of plots in the second.

Author(s)

Rachel Carroll <[e-mail]>

Loren Collingwood <[e-mail]>

Examples

library(eiExpand)
library(sf)

# load data and shps
data(planShp); data(vtd); data(mt_block_data)

# filter to a few vtds for this example
vtd <- vtd %>% 
  dplyr::filter(
    GEOID20 %in% c("30091000002", "30085000012", "30085000018", "30085000010")
  )

# run split precinct analysis without plots
spa_results <- split_precinct_analysis(
  vtd = vtd, 
  planShp = planShp, 
  block_pop_data = mt_block_data,
  vote_col_names = c('G16HALRZIN', 'G16HALDJUN', 'G16HALLBRE', 
                     'G16GOVRGIA', 'G16GOVDBUL', "G16GOVLDUN"),
  keepOrigElection = TRUE,
  generatePlots = FALSE) 

# run with plots
spa_list <- split_precinct_analysis(
  vtd = vtd, 
  planShp = planShp, 
  block_pop_data = mt_block_data,
  vote_col_names = c('G16HALRZIN', 'G16HALDJUN', 'G16HALLBRE', 
                     'G16GOVRGIA', 'G16GOVDBUL', "G16GOVLDUN"),
  lower_thresh = 0,
  keepOrigElection = TRUE,
  generatePlots = TRUE) 

# View results
spa_list[["results"]]

# View plots
#library(gridExtra)
#do.call("grid.arrange", c(spa_list[["plots"]], ncol=1))