Example of reading data from an Excel file, geocoding, simple calculations, and plotting with Leaflet

r_leaflet_readxl_example.R

library(leaflet)
library(readxl) # for read_excel()
library(ggmap) # for geocode()
library(fields) # for rdist.earth()

### read data from excel ----
# download to default working directory
download.file('https://dl.dropboxusercontent.com/u/12146012/place_names.xlsx',
              destfile='place_names.xlsx')
places <- read_excel('place_names.xlsx')

# file looks like this:
  # city            state color
  # Calgary         AB    red
  # Banff           AB    red
  # Whitefish       MT    red
  # Oakland         CA    blue
  # San Luis Obispo CA    blue
  # Brooklyn        NY    green
  # Philadelphia    NJ    green
  # Cape May        NJ    green

### geocode ----
coords <- geocode(paste0(places$city, ', ', places$state))
places <- cbind(places, coords)

### calculate center & radius for 'green' group ----
green_places <- subset(places, color=='green')
# center: mid point of lat/lon ranges
green_center <- with(green_places, c(mean(range(lon)), mean(range(lat))))
# each point's distance from the center (in meters)
green_dist_from_center <- 
  rdist.earth(t(green_center), green_places[, c('lon', 'lat')], 
              miles = FALSE) * 1000
  
# add to map ----
my_map <- leaflet() %>% 
  addTiles() %>%
  addCircleMarkers(data=places, lng= ~lon, lat= ~lat, popup= ~city, color= ~color) %>%
  addCircles(lng = green_center[1], lat = green_center[2],
             # radius = 2x center to most distant point
             radius = max(green_dist_from_center * 2),
             weight = 1, color='green', fill = 0)
             
# my_map can be seen in RStudio viewer, or embedded in html via RMarkdown
# screen shot of output: http://i.imgur.com/9pCG07y.png

Result: