Geocoding in R with Google Maps

I've tried running the code to geocode locations in R via Google Maps and the XML package from this blog post: http://www.r-chart.com/2010/07/maps-geocoding-and-r-user-conference.html

Here are his functions:

getDocNodeVal=function(doc, path){
  sapply(getNodeSet(doc, path), function(el) xmlValue(el))
}

gGeoCode=function(str){
  library(XML)
  u=paste('http://maps.google.com/maps/api/geocode/xml?sensor=false&address=',str)
  doc = xmlTreeParse(u, useInternal=TRUE)
  str=gsub(' ','%20',str)
  lng=getDocNodeVal(doc, "/GeocodeResponse/result/geometry/location/lat")
  lat=getDocNodeVal(doc, "/GeocodeResponse/result/geometry/location/lng")
  c(lat,lng)
}

When I run gGeoCode(), I get the following error:

> gGeoCode("Philadelphia, PA")
failed to load external entity "http%3A//maps.google.com/maps/api/geocode/xml%3Fsensor=false&address=%20Philadelphia,%20PA"
Error: 1: failed to load external entity "http%3A//maps.google.com/maps/api/geocode/xml%3Fsensor=false&address=%20Philadelphia,%20PA"

If I just paste into a browser the API url with Philadelphia, PA appended to the end, like the string passed to xmlParseTree, I get a result that looks like legitimate xml when I download it.

Is this an issue with the code, or have I failed to configure something or another?

Tony Breyal

Have you thought about using the json call instead? Looking at your code, you could achieve the same doing this (you'll need to install packages RCurl and RJSONIO from omegahat.com).

Copy and paste this into R:

library(RCurl)
library(RJSONIO)

construct.geocode.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))
}

gGeoCode <- function(address,verbose=FALSE) {
  if(verbose) cat(address,"\n")
  u <- construct.geocode.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
    return(c(lat, lng))
  } else {
    return(c(NA,NA))
  }
}

Here's how you use the above functions:

x <- gGeoCode("Philadelphia, PA")

This is the result you get. I think in the original code, lat and lng are mixed up? But hopefully this is what you want:

> x
[1]  39.95233 -75.16379

Hope that helps a little mate,

Tony Breyal

This code works using just the XML library

library(XML)
url = 'http://maps.googleapis.com/maps/api/geocode/xml?address=1600+Amphitheatre+Parkway,+Mountain+View,+CA&sensor=true'
doc = xmlTreeParse(url, useInternal=TRUE)
lat = as.numeric(xmlValue(getNodeSet(doc, '//location/lat')[[1]]))
lng = as.numeric(xmlValue(getNodeSet(doc, '//location/lng')[[1]]))

This is another option for geocoding - it may be easier to parse:

https://webgis.usc.edu/Services/Geocode/Default.aspx

I have modified Tony Breyal solution so that the gGeoCode function also takes a vector of addresses as input. With this version, you can not only do gGeoCode("Philadelphia, PA") but also gGeoCode(c("Philadelphia, PA","New York, NY")) with this return value.

  address            lat          lng          
1 "Philadelphia, PA" "39.952335"  "-75.163789" 
2 "New York, NY"     "40.7143528" "-74.0059731"

Note that the google maps api has a daily limit of 2,500 so that your vector shouldn't be too long. Here is the updated function:

library(RCurl)
library(RJSONIO)

construct.geocode.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))
}

gGeoCode <- function(address,verbose=FALSE) {
  require("plyr")
  if(verbose) cat(address,"\n")
  u <- aaply(address,1,construct.geocode.url)
  doc <- aaply(u,1,getURL)
  json <- alply(doc,1,fromJSON,simplify = FALSE)
  coord = laply(json,function(x) {
    if(x$status=="OK") {
      lat <- x$results[[1]]$geometry$location$lat
      lng <- x$results[[1]]$geometry$location$lng
      return(c(lat, lng))
    } else {
      return(c(NA,NA))
    }
  })
  if(length(address)>1) colnames(coord)=c("lat","lng")
  else names(coord)=c("lat","lng")
  return(data.frame(address,coord))
}

EDIT: Small correction in code so that lat and lng are returned as numerical values.

I needed to get all the returned addresses from geocode not just the first one, so I wrote a small function to do so. It can be used to geocode and to reverse geocode

geocode <- function(address,reverse=FALSE)  {
  require("RJSONIO")
  baseURL <- "http://maps.google.com/maps/api/geocode/json?sensor=false&"

  # This is not necessary, 
  # because the parameter "address" accepts both formatted address and latlng

  conURL <- ifelse(reverse,paste0(baseURL,'latlng=',URLencode(address)),
                                  paste0(baseURL,'address=',URLencode(address)))  
  con <- url(conURL)  
  data.json <- fromJSON(paste(readLines(con), collapse=""))
  close(con) 
  status <- data.json["status"]
 if(toupper(status) == "OK"){
  t(sapply(data.json$results,function(x) {
      list(address=x$formatted_address,lat=x$geometry$location[1],
                                                 lng=x$geometry$location[2])}))
 } else { 
   warning(status)
   NULL 
 }
}

Geocode example:

geocode("Dupont Cir NW, Washington, DC 20036, USA")

     address                                                               lat      lng      
[1,] "Dupont Circle Northwest, Washington, DC 20036, USA"                  38.90914 -77.04366
[2,] "Dupont Circle, 1 Dupont Circle Northwest, Washington, DC 20036, USA" 38.90921 -77.04438
[3,] "Washington, DC 20036, USA"                                           38.90808 -77.04061
[4,] "Dupont Circle, Washington, DC 20036, USA"                            38.90958 -77.04344

Reverse Geocode example:

note that the address can be either formatted address or latlng, the reverse parameter is not used but it is including for future use with other geocoding services

geocode("38.910262, -77.043565")

     address                                                    lat      lng      
[1,] "40-58 Dupont Circle Northwest, Washington, DC 20036, USA" 38.91027 -77.04357
[2,] "Washington, DC 20036, USA"                                38.90808 -77.04061
[3,] "Dupont Circle, Washington, DC, USA"                       38.90969 -77.04334
[4,] "Northwest Washington, Washington, DC, USA"                38.94068 -77.06796
[5,] "District of Columbia, USA"                                38.90598 -77.03342
[6,] "Washington, DC, USA"                                      38.90723 -77.03646
[7,] "United States"                                            37.09024 -95.71289

This can also be done with my package googleway and a valid Google Maps API key

library(googleway)

key <- "your_api_key"

df <- google_geocode("Philadelphia, PA",
                      key = key)

df$results$geometry$location
#        lat       lng
# 1 39.95258 -75.16522

And to reverse-geocode

df <- google_reverse_geocode(location = c(39.95258, -75.16522),
                             key = key)

df$results$formatted_address
# [1] "1414 PA-611, Philadelphia, PA 19102, USA"           "15th St Station - MFL, Philadelphia, PA 19102, USA"
# [3] "Center City West, Philadelphia, PA, USA"            "Center City, Philadelphia, PA, USA"                
# [5] "Philadelphia, PA, USA"                              "Philadelphia, PA 19107, USA"                       
# [7] "Philadelphia County, PA, USA"                       "Philadelphia-Camden-Wilmington, PA-NJ-DE-MD, USA"  
# [9] "Philadelphia Metropolitan Area, USA"                "Pennsylvania, USA"                                 
# [11] "United States"

来源：https://stackoverflow.com/questions/3257441/geocoding-in-r-with-google-maps

标签

google-maps

geocoding