2 min read

Put your sites on map using R

Daijiang Li · 2013/01/08

In ggmap, the x aesthetic is fixed to longitude, the y aesthetic is fixed to latitude, and the coordinate system is fixed to the Mercator projection.

In ggmap the plotting process is broken into two pieces: 1. downloading the images and formatting them for plotting, done with get_map, and 2. making the plot, done with ggmap. qmap marries these two functions for quick map plotting (c.f. ggplot2’s ggplot), and qmplot attempts to wrap up the entire plotting process into one simple command (c.f. ggplot2’s qplot).

  • get_map. In order to be consistent among different source of maps, get_map will first go to Google Map and calculate the bounding box and then clip the same map from other sources if specified.

    • The most important argument is location argument, it can be an address, longitude/latitude pair (center of the map), or left/bottom/right/top bounding box:
    • Map sources: Google Maps, OpenStreetMap, Stamen Maps, and Cloudmade Maps. For Stamen maps, maptype of watercolor and toner are different from others. toner is good for black and white mapping. Cloudmade has thousands of styles…

  • get_map will grab the map of interest, while ggmap will plot it. Sometimes you want to make your points on the map more visible, you can use darken = c(0, "black") argument. base_layer allows for faceted plots.

  • Some other nice functions.

    • geocode(). e.g. geocode(‘university of wisconsin-madison’, output=“more”).
    • revgeocode(). change coordinates (long, lat) into address.
    • mapdist(from, to). Calculate distance and driving times.
    • route().

####Example Last summer, I resampled about 34 used-be Pine Barrens sites.  Here is the distribution map:

data=read.csv("lat.csv")
library(ggplot2)
library(ggmap)
p=ggmap(get_map(c(-89.725,44.9), zoom = 7, source = "google", 
                maptype = "terrain")) #get the WI map
cbPalette <- c("blue", "red")
p+geom_point(data=data,aes(long,lat,colour = type, shape=type),
             alpha=0.8,size=4)+theme(legend.position="top")+
  scale_colour_manual(values=cbPalette)

ggmap-site

Or, another version:

library(maps)
ggplot(data, aes(long, lat))+
  borders("county","wisconsin", colour="grey70")+
  geom_point(colour="red",alpha= 0.5)+
  coord_quickmap()
# maps("state", region = c("wisconsin", "michigan:north"))

map-site