prep_hexgrid {ptools}

Creates hexagon grid cells over study area

Description

Creates hexagon grid cells of given area over particular study area.

Usage

prep_hexgrid(outline, area, clip_level = 0, point_over = NULL, point_n = 0)

Arguments

outline

SpatialPolygon or SpatialPolygonDataFrame that defines the area to draw hexgrid cells over

area

scaler for the area of the grid cells in whatever units the outline is in

clip_level

, you can clip grid cells if they are not entirely inside the outlined area, defaults to 0 so any cells at least touching are included. Specify as proportion (so should not be greater than 1!)

point_over

default NULL, but can pass in SpatialPoints and will only include grid cells that have at least one point

point_n

default 0, only used if passing in point_over. Will return only grid cells with greater than point_n points

Details

This generates a vector hex grid over the study area of interest. Hexgrids are sometimes preferred over square grid cells to prevent aliasing like artifacts in maps (runs of particular values).

Value

A SpatialPolygonDataFrame object with columns

• id, integer id value (not the same as row.names!)

• x, x centroid of grid cell

• y, y centroid of grid cell

• cover, optional (only if clip_level > 0) proportion that grid cell is covered by outline

• count, optional (only if you pass in point_over), total N of points over

References

Circo, G. M., & Wheeler, A. P. (2021). Trauma Center Drive Time Distances and Fatal Outcomes among Gunshot Wound Victims. Applied Spatial Analysis and Policy, 14(2), 379-393.

Examples

library(sp) #for sp plot methods
#Base example, some barely touch
hnyc <- prep_hexgrid(nyc_bor,area=20000^2)
plot(hnyc)
plot(nyc_bor,border='red',add=TRUE)
#Example clipping hexagons that have dongle hexagons
hex_clip <- prep_hexgrid(nyc_bor,area=20000^2,clip_level=0.3)
plot(hex_clip,border='blue')
plot(nyc_bor,border='red',add=TRUE)
summary(hnyc)

#Example clipping hexagons with no overlap crimes
hnyc <- prep_hexgrid(nyc_bor,area=4000^2,point_over=nyc_shoot)
plot(hnyc)
plot(nyc_shoot,pch='.',add=TRUE)