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Match Point Geometries to Polygon Geometries (e.g., Voter Locations to School Districts)

Source: R/Overlay.r
overlay.Rd

The overlay() function performs the "Overlay" (Step 2) operation from the QOR Method.

Usage

overlay(
  points = NULL,
  polygons = NULL,
  point_id = "point_id",
  polygon_id = "polygon_id",
  used_NCES = FALSE,
  FIPS_code = NULL,
  FIPS_col = NULL
)

Arguments

points

sf object containing point geometries for units (e.g., voter locations).

polygons

sf object containing polygon geometries (e.g., school districts).

point_id

Name of the column in the points sf object that contains unique identifiers for each point (default: "point_id"). Preferably as string.

polygon_id

Name of the column in the polygons sf object that contains unique identifiers for each polygon (default: "polygon_id"). Preferably as string.

used_NCES

Boolean indicating whether the user input NCES school district shapefiles or other shapefiles with a state FIPS_code as the polygons (default: FALSE).

FIPS_code

State FIPS code to filter NCES or other school district shapefiles (default: NULL, which means no filtering by state).

FIPS_col

Column name in your dataset containing FIPS_code. Preferably should be a character/string variable (default: NULL, which means no filtering by state).

Value

A tibble with three columns: point_id (string), polygon_id (string), and distance (based on units CRS; only for points not in just one polygon). Each point_id is matched to one polygon_id.

Details

This function:

  • Matches point geometries (e.g., voter locations) to polygon geometries (e.g., school districts) using spatial intersections and distances.

  • Requires that all points and polygons each have a unique identifier column.

  • If observations are not unique (e.g., panel data), use only one timepoint per function call (e.g., all voters in one year, then all voters in the next year, etc...).

  • Returns a match that assigns one polygon to each point: the polygon the point is in, or the closest polygon (based on internal point) if the point is not in any polygon.

  • To return multiple polygons per point, you will need to modify the code.