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How to use Google's API with R

Using Google Maps API and R

This script uses RCurl and RJSONIO to download data from Google's API to get the latitude, longitude, location type, and formatted address

library(RCurl)
library(RJSONIO)
library(plyr)

Build a URL to access the API:

url <- function(address, return.call = "json", sensor = "false") {
  root <- "http://maps.google.com/maps/api/geocode/"
  u <- paste(root, return.call, "?address=", address, "&sensor=", sensor, sep = "")
  return(URLencode(u))
}

Function to parse the results:

geoCode <- function(address,verbose=FALSE) {
  if(verbose) cat(address,"\n")
  u <- url(address)
  doc <- getURL(u)
  x <- fromJSON(doc,simplify = FALSE)
  if(x$status=="OK") {
    lat <- x$results[[1]]$geometry$location$lat
    lng <- x$results[[1]]$geometry$location$lng
    location_type  <- x$results[[1]]$geometry$location_type
    formatted_address  <- x$results[[1]]$formatted_address
    return(c(lat, lng, location_type, formatted_address))
    Sys.sleep(0.5)
  } else {
    return(c(NA,NA,NA, NA))
  }
}

Test with one address

address <- geoCode("The White House, Washington, DC")

First two items are the latitude and longitude coordinates, then the location type and formatted address

address

We can use Plyr to geocode a vector with addresses

address <- c("The White House, Washington, DC","The Capitol, Washington, DC")
locations  <- ldply(address, function(x) geoCode(x))
names(locations)  <- c("lat","lon","location_type", "formatted")
head(locations)

The following are the different location types:

  • "ROOFTOP" indicates that the returned result is a precise geocode for which we have location information accurate down to street address precision.
  • RANGE_INTERPOLATED" indicates that the returned result reflects an approximation (usually on a road) interpolated between two precise points (such as intersections). Interpolated results are generally returned when rooftop geocodes are unavailable for a street address.
  • GEOMETRIC_CENTER" indicates that the returned result is the geometric center of a result such as a polyline (for example, a street) or polygon (region).
  • APPROXIMATE" indicates that the returned result is approximate.

For more info on Google Maps API check here

@llpuente

When I insert a vector of a couple hundred addresses, a non-trivial percentage comes back as NA's. This is presumably because when the API was pinged for those particular addresses, the status came back as something other than "OK". I think this because when those same entries are inputted individually, the coordinates come out neatly. Any thoughts on how to overcome this? One thought would be to "re-ping" the API each time the status is not "OK," but am wondering how to do so most efficiently. Thanks for any thoughts!

For what it's worth, here's a fairly hackish way of overcoming this issue:

#Run loop to replace NA's created during the initial run of ldply:
for(i in 1:length(address)){
if(is.na(locations $lat[i])){
locations[i,]<-ldply(locations[i], function(x) geoCode(x))
}
}

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