hotspot_count {sfhotspot}

Count points in cells in a two-dimensional grid

Description

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.

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.

Value

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

Examples

# Set cell size automatically

hotspot_count(memphis_robberies_jan)


# Transform data to UTM zone 15N so that cell_size and bandwidth can be set
# in metres
library(sf)
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

hotspot_count(memphis_robberies_utm, cell_size = 200)