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Google Geo-coding Web Service (JSON response)
  • Difficulty Level : Hard
  • Last Updated : 19 Dec, 2017

Prerequisite : JSON Formatting in Python
Google has an excellent web service that allows us to make use of their large database of geographic information. Here, we are going to be working with the Google Maps API. In the old days, this Maps API was free and did 2, 500 requests per day but now they’ve made it so that parts of it are behind API keys and you start having to use OAuth and stuff. We can submit a geographical search string like “Ann Arbor, MI” to their geocoding API and have Google return its best guess as to where on a map we might find our search string and tell us about the landmarks nearby.

The geocoding service is free but rate limited so you cannot make unlimited use of the API in a commercial application. But if you have some survey data where an end user has entered a location in a free-format input box, you can use this API to clean up your data quite nicely.

When you are using a free API like Google’s geocoding API, you need to be respectful in your use of these resources. If too many people abuse the service, Google might drop or significantly curtail its free service.

You can read the online documentation for this service, but it is quite simple and you can even test it using a browser by typing the following URL into your browser:
http://maps.googleapis.com/maps/api/geocode/json?address=Ann+Arbor%2C+MI

Make sure to unwrap the URL and remove any spaces from the URL before pasting it into your browser.

The following is a simple application to prompt the user for a search string, call the Google geocoding API, and extract information from the returned JSON.






# Libraries used to grab the URL web stuff and import json
import urllib.request, urllib.parse, urllib.error
import json
  
# Note that Google is increasingly requiring keys
# for this API
# service URL for Google Maps API
  
while True:
    address = input('Enter location: ')
    if len(address) < 1: break
      
    # Concatenate the serviceurl and urllib.parse.urlencode
    # which give a dictonary of address equal and this bit 
    # right here
    url = serviceurl + urllib.parse.urlencode(
        {'address': address})
  
    print('Retrieving', url)
  
    # urlopen() to get a handle
    uh = urllib.request.urlopen(url)
    # Read the whole document in UTF-8
    data = uh.read().decode()
    print('Retrieved', len(data), 'characters')
  
    # Load internal strings
    try:
        js = json.loads(data)
    except:
        js = None
    # If false then quit and print data
    if not js or 'status' not in js or js['status'] != 'OK':
        print('==== Failure To Retrieve ====')
        print(data)
        continue
      
    # Call json dump and print it with an indent of four
    print(json.dumps(js, indent = 4))
      
    # Parsing and printing
    lat = js["results"][0]["geometry"]["location"]["lat"]
    lng = js["results"][0]["geometry"]["location"]["lng"]
    print('lat', lat, 'lng', lng)
    location = js['results'][0]['formatted_address']
    print(location)

Output :


Enter location: Dehradun
Retrieving http://maps.googleapis.com/maps/api/geocode/json?address=dehradun
Retrieved 1743 characters
{
    "results": [
        {
            "address_components": [
                {
                    "long_name": "Dehradun",
                    "short_name": "Dehradun",
                    "types": [
                        "locality",
                        "political"
                    ]
                },
                {
                    "long_name": "Dehradun",
                    "short_name": "Dehradun",
                    "types": [
                        "administrative_area_level_2",
                        "political"
                    ]
                },
                {
                    "long_name": "Uttarakhand",
                    "short_name": "UK",
                    "types": [
                        "administrative_area_level_1",
                        "political"
                    ]
                },
                {
                    "long_name": "India",
                    "short_name": "IN",
                    "types": [
                        "country",
                        "political"
                    ]
                }
            ],
            "formatted_address": "Dehradun, Uttarakhand, India",
            "geometry": {
                "bounds": {
                    "northeast": {
                        "lat": 30.4041936,
                        "lng": 78.1089305
                    },
                    "southwest": {
                        "lat": 30.2466633,
                        "lng": 77.92533879999999
                    }
                },
                "location": {
                    "lat": 30.3164945,
                    "lng": 78.03219179999999
                },
                "location_type": "APPROXIMATE",
                "viewport": {
                    "northeast": {
                        "lat": 30.4041936,
                        "lng": 78.1089305
                    },
                    "southwest": {
                        "lat": 30.2466633,
                        "lng": 77.92533879999999
                    }
                }
            },
            "place_id": "ChIJr4jIVsMpCTkRmYdRMsBiNUw",
            "types": [
                "locality",
                "political"
            ]
        }
    ],
    "status": "OK"
}
lat 30.3164945 lng 78.03219179999999
Dehradun, Uttarakhand, India

The program takes the search string and constructs a URL with the search string as a properly encoded parameter and then uses urllib to retrieve the text from the Google geocoding API. Unlike a fixed web page, the data we get depends on the parameters we send and the geographical data stored in Google’s servers.
Once we retrieve the JSON data, we parse it with the json library and do a few checks to make sure that we received good data, then extract the information that we are looking for.

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