Count points in cells in a two-dimensional grid

Usage

hotspot_count(
  data,
  cell_size = NULL,
  grid_type = "rect",
  grid = NULL,
  weights = NULL,
  quiet = FALSE
)

Arguments

data: sf data frame containing points.
cell_size: numeric value specifying the size of each equally spaced grid cell, using the same units (metres, degrees, etc.) as used in the sf data frame given in the data argument. Ignored if grid is not NULL. If this argument and grid are NULL (the default), the cell size will be calculated automatically (see Details).
grid_type: character specifying whether the grid should be made up of squares ("rect", the default) or hexagons ("hex"). Ignored if grid is not NULL.
grid: sf data frame containing polygons, which will be used as the grid for which counts are made.
weights: NULL or the name of a column in data to be used as weights for weighted counts.
quiet: if set to TRUE, messages reporting the values of any parameters set automatically will be suppressed. The default is FALSE.

Value

An sf tibble of regular grid cells with corresponding point counts for each cell. This can be plotted using autoplot.

Details

This function counts the number of points in each cell in a regular grid. If a column name in data is supplied with the weights argument, weighted counts will also be produced.

Automatic cell-size selection

If grid is NULL and no cell size is given, the cell size will be set so that there are 50 cells on the shorter side of the grid. If the data SF object is projected in metres or feet, the number of cells will be adjusted upwards so that the cell size is a multiple of 100.

Examples


# Set cell size automatically
# \donttest{
hotspot_count(memphis_robberies_jan)
#> Cell size set to 0.00512 degrees automatically
#> Simple feature collection with 2505 features and 1 field
#> Geometry type: POLYGON
#> Dimension:     XY
#> Bounding box:  xmin: -90.1261 ymin: 34.99475 xmax: -89.77282 ymax: 35.25587
#> Geodetic CRS:  WGS 84
#> # A tibble: 2,505 × 2
#>        n                                                                geometry
#>  * <dbl>                                                           <POLYGON [°]>
#>  1     0 ((-90.03394 34.99475, -90.02882 34.99475, -90.02882 34.99987, -90.0339…
#>  2     0 ((-90.02882 34.99475, -90.0237 34.99475, -90.0237 34.99987, -90.02882 …
#>  3     0 ((-90.0237 34.99475, -90.01858 34.99475, -90.01858 34.99987, -90.0237 …
#>  4     0 ((-90.01858 34.99475, -90.01346 34.99475, -90.01346 34.99987, -90.0185…
#>  5     1 ((-90.01346 34.99475, -90.00834 34.99475, -90.00834 34.99987, -90.0134…
#>  6     0 ((-90.00834 34.99475, -90.00322 34.99475, -90.00322 34.99987, -90.0083…
#>  7     0 ((-90.00322 34.99475, -89.9981 34.99475, -89.9981 34.99987, -90.00322 …
#>  8     0 ((-89.9981 34.99475, -89.99298 34.99475, -89.99298 34.99987, -89.9981 …
#>  9     0 ((-89.99298 34.99475, -89.98786 34.99475, -89.98786 34.99987, -89.9929…
#> 10     0 ((-90.05442 34.99987, -90.0493 34.99987, -90.0493 35.00499, -90.05442 …
#> # ℹ 2,495 more rows
# }

# Transform data to UTM zone 15N so that cell_size and bandwidth can be set
# in metres
library(sf)
#> Linking to GEOS 3.11.0, GDAL 3.5.3, PROJ 9.1.0; sf_use_s2() is TRUE
memphis_robberies_utm <- st_transform(memphis_robberies_jan, 32615)

# Manually set grid-cell size in metres, since the `memphis_robberies_utm`
# dataset uses a co-ordinate reference system (UTM zone 15 north) that is
# specified in metres
# \donttest{
hotspot_count(memphis_robberies_utm, cell_size = 200)
#> Simple feature collection with 16133 features and 1 field
#> Geometry type: POLYGON
#> Dimension:     XY
#> Bounding box:  xmin: 762136.2 ymin: 3876586 xmax: 794136.2 ymax: 3905386
#> Projected CRS: WGS 84 / UTM zone 15N
#> # A tibble: 16,133 × 2
#>        n                                                                geometry
#>  * <dbl>                                                           <POLYGON [m]>
#>  1     0 ((771936.2 3876586, 771936.2 3876786, 772136.2 3876786, 772136.2 38765…
#>  2     0 ((772136.2 3876586, 772136.2 3876786, 772336.2 3876786, 772336.2 38765…
#>  3     0 ((772336.2 3876586, 772336.2 3876786, 772536.2 3876786, 772536.2 38765…
#>  4     0 ((772536.2 3876586, 772536.2 3876786, 772736.2 3876786, 772736.2 38765…
#>  5     1 ((772736.2 3876586, 772736.2 3876786, 772936.2 3876786, 772936.2 38765…
#>  6     0 ((772936.2 3876586, 772936.2 3876786, 773136.2 3876786, 773136.2 38765…
#>  7     0 ((773136.2 3876586, 773136.2 3876786, 773336.2 3876786, 773336.2 38765…
#>  8     0 ((773336.2 3876586, 773336.2 3876786, 773536.2 3876786, 773536.2 38765…
#>  9     0 ((773536.2 3876586, 773536.2 3876786, 773736.2 3876786, 773736.2 38765…
#> 10     0 ((771136.2 3876786, 771136.2 3876986, 771336.2 3876986, 771336.2 38767…
#> # ℹ 16,123 more rows
# }