Map an ACS variable by tract in a drive-time area (map 3 of 4)

Draws an interactive leaflet map of one American Community Survey (ACS) variable over the census tracts that overlap a drive-time area of a site. The part of each tract inside the area is shaded by the tract's estimate as it is in acs_sf, before any weighting. The outline of the area and the site's point are drawn on top.

Usage

cacs_plot_site_weighted(
  site_id = NULL,
  lat = NULL,
  lon = NULL,
  site_name = NULL,
  iso_sf,
  tract_sf,
  acs_sf,
  sites_df = NULL,
  variable = "B17001_002",
  tiles = "OpenStreetMap",
  padding_km = 5,
  drive_time_min = NULL,
  variable_family = "spatial_total",
  ...
)

Arguments

site_id: A string giving the site_id of the site to map, used to find its point in sites_df and its drive-time areas in iso_sf.
lat, lon: Single numbers giving the latitude and longitude of a point in degrees (WGS 84), used when site_id is NULL. Both must be given. The point is marked at that location, and the areas of every site in iso_sf are used.
site_name: A string giving the name of the site, compared with the site_name column of sites_df including case, and used when site_id, lat, and lon are NULL. It must match one row.
iso_sf: An sf object of drive-time areas in EPSG:4326 (longitude and latitude), such as the result of cacs_isochrone(), with the columns site_id and drive_time_min.
tract_sf: An sf object of census tract polygons with a GEOID column, such as the result of cacs_acs_prefetch(). When a tract has several rows, as in that result (one for each variable), the first row is used.
acs_sf: A data frame or sf object of tract estimates in the long form of the result of cacs_acs_prefetch(), with the columns GEOID, variable, estimate, and moe. It is often the same object as tract_sf. The estimates are mapped as they are: unlike cacs_intersect_weight(), the map does not set Census Bureau annotation codes, such as -666666666, to NA, and it draws a tract with two rows for the variable twice instead of giving an error.
sites_df: An sf object of site points in longitude and latitude with a site_id column, or NULL (the default) for cacs_alabama_sites. The bundled file legacy_2025_isochrones.rds uses the same site_id values for other places, so with its areas the default puts the point and the initial view far from them.
variable: A string giving the ACS variable code to map, one of the values in the variable column of acs_sf. The default is "B17001_002", the number of people whose income in the past 12 months was below the poverty level.
tiles: A string naming the background map, one of the tile providers in leaflet::providers; the default is "OpenStreetMap", the standard OpenStreetMap map, which needs no API key. The map is built offline, and the tiles are downloaded when it is displayed. The CARTO tiles, such as "CartoDB.Positron", need an API key, which these functions do not send, so they show a notice asking for one.
padding_km: A single positive number. The initial view shows at least this many kilometers on each side of the site; the default is 5.
drive_time_min: A single number giving the drive time, in minutes, of the area to map, or NULL (the default) for the longest drive time of the site in iso_sf. It must be one of the drive times in iso_sf.
variable_family: A string giving the kind of quantity that variable is, as in the estimand_family column of cacs_run() results. It only chooses the ColorBrewer palette: "Greens" for "spatial_total" (a count; the default), "PuOr" for "median_proxy" (a median), "YlOrRd" for "area_weighted_scalar_proxy" (a per-person value), and "RdYlBu" for "derived_rate" (a rate). NA and unrecognized values give "YlGnBu", and "metadata_only" gives an error. The value is not checked against variable.
...: Not used. Any argument given here is ignored.

Value

A leaflet map (an HTML widget).

Details

Clicking a tract shows the values that cacs_plot_site_intersection() shows: GEOID, the coverage weight area_wt (the share of the tract's area inside the drive-time area), and intersection_km2 (the area of that part in square kilometers), with the variable code. It also shows the tract's estimate, its margin of error (moe, the half-width of the 90 percent confidence interval published with the estimate), and the coverage weight times the estimate, labeled "area_wt x estimate". For a count, the products add up to the estimate that cacs_intersect_weight() gives for the area, which is NA when any tract's estimate is missing. For a median or a per-person value, that estimate is instead an average of the tract estimates weighted by area shares (see cacs_intersect_weight()), and the products do not add up to it.

The estimates are grouped into color classes by natural breaks when the classInt package is installed and there are at least five different estimates, and by pretty() otherwise. A tract with a missing estimate, or with no row for variable in acs_sf, is gray.

With lat and lon instead of site_id, the rows of iso_sf are not narrowed to one site. The drive time is then chosen among the drive times of all the sites in iso_sf, and the area of every site for that drive time is drawn, so a map of one area needs an iso_sf that holds the rows of one site. cacs_plot_site_rates() and cacs_plot_site_pipeline() differ: they map the site in sites_df nearest to the point.

Examples

if (requireNamespace("leaflet", quietly = TRUE)) {
  # Example data bundled with the package for one site in Birmingham,
  # Alabama: a 10-minute drive-time area from the OSRM routing service,
  # 2019-2023 ACS estimates for nearby tracts, and the cacs_run() result.
  fx <- readRDS(system.file("extdata", "visual_walkthrough_fixture.rds",
                            package = "catchmentACS"))
  # Median household income, a median
  cacs_plot_site_weighted(site_id = "AL_BHM_01", iso_sf = fx$iso_sf,
                          tract_sf = fx$tract_sf, acs_sf = fx$acs_sf,
                          variable = "B19013_001",
                          variable_family = "median_proxy",
                          sites_df = fx$sites_df)
}

Usage

Arguments

Value

Details

See also

Examples