library(qmap)
library(ggmap)

## FROM ?ggmap :

# a shapefile like layer
data(zips)
ggmap(get_map(maptype = 'satellite', zoom = 8), extent = 'device') +
  geom_polygon(aes(x = lon, y = lat, group = plotOrder),
    data = zips, colour = NA, fill = 'red', alpha = .2) +
  geom_path(aes(x = lon, y = lat, group = plotOrder),
    data = zips, colour = 'white', alpha = .4, size = .4)


# -------

# AND THIS! 

library(plyr)
zipsLabels <- ddply(zips, .(zip), function(df){
  df[1,c("area", "perimeter", "zip", "lonCent", "latCent")]
})
ggmap(get_map(maptype = 'satellite', zoom = 9),
    extent = 'device', legend = 'none', darken = .5) +
  geom_text(aes(x = lonCent, y = latCent, label = zip, size = area),
    data = zipsLabels, colour = I('red')) +
  scale_size(range = c(1.5,6))
  
  
# -------