Geocoding With R’s ggmap Package

One of the great pieces of the new ggmap package is the geocoding functionality. Other R functions can be used to geocode but they fail to provide detailed output like geocode accuracy which is often critical. You need to know if the lat/long in the output refers to a rooftop location or a city center, for example. In the past, our work around has been to use Python (e.g., the module pygeocoder) which allows us to get detailed output. But ggmap makes this even easier.

For example, you could simply type the following to grab coordinates:

library(ggmap)
geocode("someplace, nyc")
##      lon   lat
## 1 -74.01 40.71

But this won't tell you what the coordinates refer to. Without additional detail you might assume that this would be a good geocode. To address this ggmap provides some alternatives using the output argument. For example:

geocode("someplace, nyc", output = "more")
##      lon   lat     type     loctype           address north south  east
## 1 -74.01 40.71 locality approximate new york, ny, usa 40.92  40.5 -73.7
##     west postal_code       country administrative_area_level_2
## 1 -74.26        <NA> united states             new york county
##   administrative_area_level_1 locality street streetNo point_of_interest
## 1                    new york new york   <NA>       NA              <NA>
##            query
## 1 someplace, nyc

Pay particular attention to loctype in the output where you can see that this particular geocode is only approximate. Approximate may not be accurate enough depending on your project. Let's try a real address:

# address for the empire state building
mygeocode <- geocode("350 5th Ave, New York, NY 10118", output = "more")
mygeocode$loctype
## [1] rooftop
## Levels: rooftop

Here we see a rooftop geocode, a geocode we can have much more confidence in. Now let's try mapping:

qmap(location = c(lon = mygeocode$lon, lat = mygeocode$lat), zoom = 17, maptype = "satellite")

plot of chunk unnamed-chunk-4

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