Create heatmap polygons shapefile from a points shapefile for a variable in attribute table in R

Question

The objective is to create heatmap polygons from a points shapefile named "df_sf" for an attribute "V1" in the shapefile and then export these polygons as another shapefile in R.

What I have tried?

1. I have implemented the script here to generate density plots for the points using Lat and Long data not the variable "V1" value: Create density polygons from spatial points in R

2. tmaps cannot be exported as shapefile and the code below does not create polygons

p1 <- st_read("spatialdata.shp")

df_sf <- sf::st_as_sf(p1)

# Install and load required packages
install.packages(c("sf", "dplyr", "tmap", "sfheaders"))
library(sf)
library(dplyr)
library(tmap)
library(sfheaders)

# Create heatmap polygons
heatmap_polygons <- df_sf %>%
  st_transform(st_crs(4326)) %>%
  tm_shape() +
  tm_dots(col = "V1", palette = "Reds", size = 0.1, alpha = 0.5) +
  tm_layout()

tm_view(legend.position = c("right", "bottom"))

tmap_leaflet(heatmap_polygons)

st_write(heatmap_sf, "heatmap_polygons.shp")

Error: Error in UseMethod("st_write") : 
  no applicable method for 'st_write' applied to an object of class "tmap"

Answer 1

More correct nomenclature is that you want to calculate the kernel density of your points then create a polygon based on a contour of the resulting density. An easy way to think contour in this regard is using the percent volume (eg., what data is contained within the 60% volume of the data). This is common in deriving resource selection in species movement (telemetry) models. Here is a quick worked example.

Add libraries and create example data

library(sf)
library(spatialEco)
library(terra)

e <- rast(system.file("extdata/elev.tif", package="spatialEco"))
poly <- bbox_poly(e) 
p <- st_sf(st_sample(poly, size=100))

Now, we calculate the density of the points, calculate the percent volume contour and coerce to polygon.

d <- sf.kde(p, res = 1000) # KDE
v <- raster.vol(d, 0.60)   # volume contour
  v[v == 0] <- NA
vpoly <- st_as_sf(as.polygons(v))

plot(d, legend=FALSE)
  plot(vpoly, add=TRUE, col=NA)
  plot(p, pch=20, add=TRUE)