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
