Script for Creating Leaflet Map of Population Density in St. Louis

leaflet-example.R

# dependencies
library(dplyr)     # data wrangling
library(classInt)  # calculate breaks
library(leaflet)   # leaflet maps
library(sf)        # spatial data tools
library(stringr)   # work with strings

# load data and re-project to WGS 1984
st_read("STL_DEMOS_Nhoods.shp", stringsAsFactors = FALSE) %>%
    st_transform(crs = 4326) -> popChange

# calculate population density
popChange <- mutate(popChange, pop17_den = pop17/(AREA/1000000))

# create breaks
cp_bins <- function(.data, var, n = 5, style = "jenks", round = 0, dig = 10){
    
  # calculate breaks
  breaks <- classIntervals(.data[[var]], n = n, style = style)
  categories <- cut(.data[[var]], breaks = c(breaks$brks), include.lowest = TRUE, dig.lab = dig)
  
  # parse categories
  categories <- unique(categories)
  categories <- gsub("[][()]", "", categories)
  categories <- gsub(",", " ", categories)
  categories <- word(categories, 2)
  categories <- round(as.numeric(categories), digits = round)
  bins <- c(0, categories)
  
  # return output
  return(bins)
  
}

# calculate breaks
bins <- cp_bins(popChange, var = "pop17_den")

# create color palette
pal <- colorBin("YlGnBu", domain = popChange$pop17_den, bins = bins)

# create map
popChange %>%
  leaflet() %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  addPolygons(
    color = "#444444", 
    weight = 1, 
    opacity = 1.0, 
    smoothFactor = 0.5,
    fillOpacity = 0.5,
    fillColor = ~pal(pop17_den),
    highlightOptions = highlightOptions(color = "white", weight = 2, bringToFront = TRUE),
    popup = paste("<b>Name:</b> ", popChange$NHD_NAME, "<br>",
                  "<b>2017 Population:</b> ", round(popChange$pop17, digits = 0), "<br>",
                  "<b>2017 Population Density (per Km^2):</b> ", 
                      round((popChange$pop17_den), digits = 0),"<br>",
                  "<b>Area (Km^2):</b> ", round(popChange$AREA/1000000, digits = 2))) %>%
    addLegend(pal = pal, values = ~pop17_den, opacity = .5, title = "Population Density (2017)")
    
    
# data for this example can be found here - https://github.com/slu-soc5650/lecture-05/tree/master/data/example-data/STL_DEMOS_Nhoods