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Find all Census blocks in a polygon, using internal point of block

Source: R/get_blockpoints_in_shape.R
get_blockpoints_in_shape.Rd

Like getblocksnearby(), but for blocks in each polygon rather than blocks near each facility. For analyzing all residents in certain zones such as places at elevated risk, redlined areas, watersheds, etc.

Usage

get_blockpoints_in_shape(
  polys,
  addedbuffermiles = 0,
  blocksnearby = NULL,
  dissolved = FALSE,
  safety_margin_ratio = 1.1,
  crs = 4269,
  updateProgress = NULL
)

Arguments

polys

Spatial data as from sf::st_as_sf(), with points as from shapefile_from_sitepoints(), or a table of points with lat,lon columns that will first be converted here using that function, or polygons

addedbuffermiles

width of optional buffering to add to the points (or edges), in miles

blocksnearby

optional table of blocks with blockid, etc (from which lat,lon can be looked up in blockpoints dt)

dissolved

If TRUE, use sf::st_union(polys) to find unique blocks inside any one or more of polys

safety_margin_ratio

multiplied by addedbuffermiles, how far to search for blocks nearby using getblocksnearby(), before using those found to do the intersection via sf::

crs

used in st_as_sf() and st_transform() and shape_buffered_from_shapefile_points(), crs = 4269 or Geodetic CRS NAD83

updateProgress

optional Shiny progress bar to update

Value

Block points table for those blocks whose internal point is inside the buffer which is just a circular buffer of specified radius if polys are just points.

Details

This uses getblocksnearby() to get a very fast rough/good estimate of which US block points are nearby (with a safety margin - see param below), before then using sf:: to carefully identify which of those candidate blocks are actually inside each polygon (e.g., circle) according to sf:: methods.

For circular buffers, just using getblocksnearby() should work and not need this function.

For noncircular polygons, buffered or not, this function will provide a way to very quickly filter down to which of the millions of US blocks should be examined by the sf:: join / intersect, since otherwise it takes forever for sf:: to check all US blocks.

See also

get_blockpoints_in_shape() shapefile_from_sitepoints() shape_buffered_from_shapefile_points()

Examples

  # y <- get_blockpoints_in_shape()

  # x = shapefile_from_sitepoints(testpoints_n(2))
  # y = get_blockpoints_in_shape(x, 1)  # very very slow