Geocoder

Geocoder is a complete geocoding solution for Ruby. With Rails it adds geocoding (by street or IP address), reverse geocoding (find street address based on given coordinates), and distance queries. It's as simple as calling geocode on your objects, and then using a scope like Venue.near("Billings, MT").

Compatibility

Installation

Install Geocoder like any other Ruby gem:

gem install geocoder

Or, if you're using Rails/Bundler, add this to your Gemfile:

gem "geocoder"

and run at the command prompt:

bundle install

Object Geocoding

ActiveRecord

Your model must have two attributes (database columns) for storing latitude and longitude coordinates. By default they should be called latitude and longitude but this can be changed (see "Model Configuration" below):

rails generate migration AddLatitudeAndLongitudeToModel latitude:float longitude:float
rake db:migrate

For reverse geocoding your model must provide a method that returns an address. This can be a single attribute, but it can also be a method that returns a string assembled from different attributes (eg: city, state, and country).

Next, your model must tell Geocoder which method returns your object's geocodable address:

geocoded_by :full_street_address   # can also be an IP address
after_validation :geocode          # auto-fetch coordinates

For reverse geocoding, tell Geocoder which attributes store latitude and longitude:

reverse_geocoded_by :latitude, :longitude
after_validation :reverse_geocode  # auto-fetch address

Mongoid

First, your model must have an array field for storing coordinates:

field :coordinates, :type => Array

You may also want an address field, like this:

field :address

but if you store address components (city, state, country, etc) in separate fields you can instead define a method called address that combines them into a single string which will be used to query the geocoding service.

Once your fields are defined, include the Geocoder::Model::Mongoid module and then call geocoded_by:

include Geocoder::Model::Mongoid
geocoded_by :address               # can also be an IP address
after_validation :geocode          # auto-fetch coordinates

Reverse geocoding is similar:

include Geocoder::Model::Mongoid
reverse_geocoded_by :coordinates
after_validation :reverse_geocode  # auto-fetch address

Once you've set up your model you'll need to create the necessary spatial indices in your database:

rake db:mongoid:create_indexes

Be sure to read Latitude/Longitude Order in the Notes on MongoDB section below on how to properly retrieve latitude/longitude coordinates from your objects.

MongoMapper

MongoMapper is very similar to Mongoid, just be sure to include Geocoder::Model::MongoMapper.

Mongo Indices

By default, the methods geocoded_by and reverse_geocoded_by create a geospatial index. You can avoid index creation with the :skip_index option, for example:

include Geocoder::Model::Mongoid
geocoded_by :address, :skip_index => true

Bulk Geocoding

If you have just added geocoding to an existing application with a lot of objects you can use this Rake task to geocode them all:

rake geocode:all CLASS=YourModel

Geocoder will print warnings if you exceed the rate limit for your geocoding service. Some services — Google notably — enforce a per-second limit in addition to a per-day limit. To avoid exceeding the per-second limit, you can add a sleep option to the rake task, like so:

rake geocode:all CLASS=YourModel sleep=0.25

Request Geocoding by IP Address

Geocoder adds a location method to the standard Rack::Request object so you can easily look up the location of any HTTP request by IP address. For example, in a Rails controller or a Sinatra app:

# returns Geocoder::Result object
result = request.location

Note that this will usually return nil in your test and development environments because things like "localhost" and "0.0.0.0" are not an Internet IP addresses.

See Advanced Geocoding below for more information about Geocoder::Result objects.

Location-Aware Database Queries

To find objects by location, use the following scopes:

Venue.near('Omaha, NE, US', 20)    # venues within 20 miles of Omaha
Venue.near([40.71, 100.23], 20)    # venues within 20 miles of a point
Venue.near([40.71, 100.23], 20, :units => :km)
                                   # venues within 20 kilometres of a point
Venue.geocoded                     # venues with coordinates
Venue.not_geocoded                 # venues without coordinates

With geocoded objects you can do things like this:

if obj.geocoded?
  obj.nearbys(30)                      # other objects within 30 miles
  obj.distance_from([40.714,-100.234]) # distance from arbitrary point to object
  obj.bearing_to("Paris, France")      # direction from object to arbitrary point
end

Some utility methods are also available:

# look up coordinates of some location (like searching Google Maps)
Geocoder.coordinates("25 Main St, Cooperstown, NY")
 => [42.700149, -74.922767]

# distance (in miles) between Eiffel Tower and Empire State Building
Geocoder::Calculations.distance_between([47.858205,2.294359], [40.748433,-73.985655])
 => 3619.77359999382

# find the geographic center (aka center of gravity) of objects or points
Geocoder::Calculations.geographic_center([city1, city2, [40.22,-73.99], city4])
 => [35.14968, -90.048929]

Please see the code for more methods and detailed information about arguments (eg, working with kilometers).

Distance and Bearing

When you run a location-aware query the returned objects have two attributes added to them (only w/ ActiveRecord):

Results are automatically sorted by distance from the search point, closest to farthest. Bearing is given as a number of clockwise degrees from due north, for example:

You can convert these numbers to compass point names by using the utility method provided:

Geocoder::Calculations.compass_point(355) # => "N"
Geocoder::Calculations.compass_point(45)  # => "NE"
Geocoder::Calculations.compass_point(208) # => "SW"

Note: when using SQLite distance and bearing values are provided for interface consistency only. They are not very accurate.

To calculate accurate distance and bearing with SQLite or MongoDB:

obj.distance_to([43.9,-98.6])  # distance from obj to point
obj.bearing_to([43.9,-98.6])   # bearing from obj to point
obj.bearing_from(obj2)         # bearing from obj2 to obj

The bearing_from/to methods take a single argument which can be: a [lat,lon] array, a geocoded object, or a geocodable address (string). The distance_from/to methods also take a units argument (:mi, :km, or :nm for nautical miles).

Model Configuration

You are not stuck with using the latitude and longitude database column names (with ActiveRecord) or the coordinates array (Mongo) for storing coordinates. For example:

geocoded_by :address, :latitude  => :lat, :longitude => :lon # ActiveRecord
geocoded_by :address, :coordinates => :coords                # MongoDB

The address method can return any string you'd use to search Google Maps. For example, any of the following are acceptable:

If your model has street, city, state, and country attributes you might do something like this:

geocoded_by :address

def address
  [street, city, state, country].compact.join(', ')
end

For reverse geocoding you can also specify an alternate name attribute where the address will be stored, for example:

reverse_geocoded_by :latitude, :longitude, :address => :location  # ActiveRecord
reverse_geocoded_by :coordinates, :address => :loc                # MongoDB

Advanced Querying

When querying for objects (if you're using ActiveRecord) you can also look within a square rather than a radius (circle) by using the within_bounding_box scope:

distance = 20
center_point = [40.71, 100.23]
box = Geocoder::Calculations.bounding_box(center_point, distance)
Venue.within_bounding_box(box)

This can also dramatically improve query performance, especially when used in conjunction with indexes on the latitude/longitude columns. Note, however, that returned results do not include distance and bearing attributes. Note that #near performs both bounding box and radius queries for speed.

Advanced Geocoding

So far we have looked at shortcuts for assigning geocoding results to object attributes. However, if you need to do something fancy you can skip the auto-assignment by providing a block (takes the object to be geocoded and an array of Geocoder::Result objects) in which you handle the parsed geocoding result any way you like, for example:

reverse_geocoded_by :latitude, :longitude do |obj,results|
  if geo = results.first
    obj.city    = geo.city
    obj.zipcode = geo.postal_code
    obj.country = geo.country_code
  end
end
after_validation :reverse_geocode

Every Geocoder::Result object, result, provides the following data:

If you're familiar with the results returned by the geocoding service you're using you can access even more data, but you'll need to be familiar with the particular Geocoder::Result object you're using and the structure of your geocoding service's responses. (See below for links to geocoding service documentation.)

Geocoding Services

By default Geocoder uses Google's geocoding API to fetch coordinates and street addresses (FreeGeoIP is the default for IP address info). However there are several other APIs supported, as well as a variety of settings. Please see the listing and comparison below for details on specific geocoding services (not all settings are supported by all services). Some common configuration options are:

# config/initializers/geocoder.rb
Geocoder.configure(

  # geocoding service (see below for supported options):
  :lookup => :yandex,

  # to use an API key:
  :api_key => "...",

  # geocoding service request timeout, in seconds (default 3):
  :timeout => 5,

  # set default units to kilometers:
  :units => :km,

  # caching (see below for details):
  :cache => Redis.new,
  :cache_prefix => "..."

)

Please see lib/geocoder/configuration.rb for a complete list of configuration options. Additionally, some lookups have their own configuration options, some of which are directly supported by Geocoder. For example, to specify a value for Google's bounds parameter:

# with Google:
Geocoder.search("Paris", :bounds => [[32.1,-95.9], [33.9,-94.3]])

Please see the source code for each lookup to learn about directly supported parameters. Parameters which are not directly supported can be specified using the :params option, by which you can pass arbitrary parameters to any geocoding service. For example, to use Nominatim's countrycodes parameter:

# with Nominatim:
Geocoder.search("Paris", :params => {:countrycodes => "gb,de,fr,es,us"})

Listing and Comparison

The following is a comparison of the supported geocoding APIs. The "Limitations" listed for each are a very brief and incomplete summary of some special limitations beyond basic data source attribution. Please read the official Terms of Service for a service before using it.

Google (:google, :google_premier)

Yahoo BOSS (:yahoo)

Yahoo BOSS is not a free service. As of November 17, 2012 Yahoo no longer offers a free geocoding API.

Bing (:bing)

Nominatim (:nominatim)

Yandex (:yandex)

Geocoder.ca (:geocoder_ca)

Mapquest (:mapquest)

Ovi/Nokia (:ovi)

ESRI (:esri)

Data Science Toolkit (:dstk)

Data Science Toolkit provides an API whose reponse format is like Google's but which can be set up as a privately hosted service.

FreeGeoIP (:freegeoip)

MaxMind Web Services (:maxmind)

Caching

It's a good idea, when relying on any external service, to cache retrieved data. When implemented correctly it improves your app's response time and stability. It's easy to cache geocoding results with Geocoder, just configure a cache store:

Geocoder.configure(:cache => Redis.new)

This example uses Redis, but the cache store can be any object that supports these methods:

Even a plain Ruby hash will work, though it's not a great choice (cleared out when app is restarted, not shared between app instances, etc).

You can also set a custom prefix to be used for cache keys:

Geocoder.configure(:cache_prefix => "...")

By default the prefix is geocoder:

If you need to expire cached content:

Geocoder.cache.expire("http://...") # expire cached result for a URL
Geocoder.cache.expire(:all)         # expire all cached results

Do not include the prefix when passing a URL to be expired. Expiring :all will only expire keys with the configured prefix (won't kill every entry in your key/value store).

For an example of a cache store with URL expiry please see examples/autoexpire_cache.rb

Before you implement caching in your app please be sure that doing so does not violate the Terms of Service for your geocoding service.

Forward and Reverse Geocoding in the Same Model

If you apply both forward and reverse geocoding functionality to the same model (say users can supply an address or coordinates and you want to fill in whatever's missing), you will provide two address methods:

For example:

class Venue

  # build an address from street, city, and state attributes
  geocoded_by :address_from_components

  # store the fetched address in the full_address attribute
  reverse_geocoded_by :latitude, :longitude, :address => :full_address
end

However, there can be only one set of latitude/longitude attributes, and whichever you specify last will be used. For example:

class Venue

  geocoded_by :address,
    :latitude  => :fetched_latitude,  # this will be overridden by the below
    :longitude => :fetched_longitude  # same here

  reverse_geocoded_by :latitude, :longitude
end

The reason for this is that we don't want ambiguity when doing distance calculations. We need a single, authoritative source for coordinates!

Once both forward and reverse geocoding has been applied, it is possible to call them sequentially.

For example:

class Venue

  after_validation :geocode, :reverse_geocode

end

For certain geolocation services such as Google geolocation API this may cause issues during subsequent updates to database records if the longtitude and latitude coordinates cannot be associated known location address (on a large body of water for example). On subsequent callbacks the following call:

 after_validation :geocode

will alter the longtitude and latitude attributes based on the location field, which would be the closest known location to the original coordinates. In this case it is better to add conditions to each call, as not to override coordinates that do not have known location addresses associated with them.

For example:

class Venue

  after_validation :reverse_geocode, :if => :has_coordinates
  after_validation :geocode, :if => :has_location, :unless => :has_coordinates

end  

Use Outside of Rails

You can use Geocoder outside of Rails by calling the Geocoder.search method:

results = Geocoder.search("McCarren Park, Brooklyn, NY")

This returns an array of Geocoder::Result objects with all data provided by the geocoding service.

Testing Apps that Use Geocoder

When writing tests for an app that uses Geocoder it may be useful to avoid network calls and have Geocoder return consistent, configurable results. To do this, configure and use the :test lookup. For example:

Geocoder.configure(:lookup => :test)

Geocoder::Lookup::Test.add_stub(
  "New York, NY", [
    {
      'latitude'     => 40.7143528,
      'longitude'    => -74.0059731,
      'address'      => 'New York, NY, USA',
      'state'        => 'New York',
      'state_code'   => 'NY',
      'country'      => 'United States',
      'country_code' => 'US'
    }
  ]
)

Now, any time Geocoder looks up "New York, NY" its results array will contain one result with the above attributes. You can also set a default stub:

Geocoder.configure(:lookup => :test)

Geocoder::Lookup::Test.set_default_stub(
  [
    {
      'latitude'     => 40.7143528,
      'longitude'    => -74.0059731,
      'address'      => 'New York, NY, USA',
      'state'        => 'New York',
      'state_code'   => 'NY',
      'country'      => 'United States',
      'country_code' => 'US'
    }
  ]
)

Any query that hasn't been explicitly stubbed will return that result.

Command Line Interface

When you install the Geocoder gem it adds a geocode command to your shell. You can search for a street address, IP address, postal code, coordinates, etc just like you can with the Geocoder.search method for example:

$ geocode 29.951,-90.081
Latitude:         29.952211
Longitude:        -90.080563
Full address:     1500 Sugar Bowl Dr, New Orleans, LA 70112, USA
City:             New Orleans
State/province:   Louisiana
Postal code:      70112
Country:          United States
Google map:       http://maps.google.com/maps?q=29.952211,-90.080563

There are also a number of options for setting the geocoding API, key, and language, viewing the raw JSON reponse, and more. Please run geocode -h for details.

Numeric Data Types and Precision

Geocoder works with any numeric data type (e.g. float, double, decimal) on which trig (and other mathematical) functions can be performed.

A summary of the relationship between geographic precision and the number of decimal places in latitude and longitude degree values is available on Wikipedia. As an example: at the equator, latitude/longitude values with 4 decimal places give about 11 metres precision, whereas 5 decimal places gives roughly 1 metre precision.

Notes on MongoDB

The Near Method

Mongo document classes (Mongoid and MongoMapper) have a built-in near scope, but since it only works two-dimensions Geocoder overrides it with its own spherical near method in geocoded classes.

Latitude/Longitude Order

Coordinates are generally printed and spoken as latitude, then longitude ([lat,lon]). Geocoder respects this convention and always expects method arguments to be given in [lat,lon] order. However, MongoDB requires that coordinates be stored in [lon,lat] order as per the GeoJSON spec (http://geojson.org/geojson-spec.html#positions), so internally they are stored "backwards." However, this does not affect order of arguments to methods when using Mongoid or MongoMapper.

To access an object's coordinates in the conventional order, use the to_coordinates instance method provided by Geocoder. For example:

obj.to_coordinates  # => [37.7941013, -122.3951096] # [lat, lon]

Calling obj.coordinates directly returns the internal representation of the coordinates which, in the case of MongoDB, is probably the reverse of what you want:

obj.coordinates     # => [-122.3951096, 37.7941013] # [lon, lat]

For consistency with the rest of Geocoder, always use the to_coordinates method instead.

Notes on Non-Rails Frameworks

If you are using Geocoder with ActiveRecord and a framework other than Rails (like Sinatra or Padrino) you will need to add this in your model before calling Geocoder methods:

extend Geocoder::Model::ActiveRecord 

Optimisation of Distance Queries

In MySQL and Postgres the finding of objects near a given point is speeded up by using a bounding box to limit the number of points over which a full distance calculation needs to be done.

To take advantage of this optimisation you need to add a composite index on latitude and longitude. In your Rails migration:

add_index :table, [:latitude, :longitude]

Distance Queries in SQLite

SQLite's lack of trigonometric functions requires an alternate implementation of the near scope. When using SQLite, Geocoder will automatically use a less accurate algorithm for finding objects near a given point. Results of this algorithm should not be trusted too much as it will return objects that are outside the given radius, along with inaccurate distance and bearing calculations.

Discussion

There are few options for finding objects near a given point in SQLite without installing extensions:

  1. Use a square instead of a circle for finding nearby points. For example, if you want to find points near 40.71, 100.23, search for objects with latitude between 39.71 and 41.71 and longitude between 99.23 and 101.23. One degree of latitude or longitude is at most 69 miles so divide your radius (in miles) by 69.0 to get the amount to add and subtract from your center coordinates to get the upper and lower bounds. The results will not be very accurate (you'll get points outside the desired radius), but you will get all the points within the required radius.

  2. Load all objects into memory and compute distances between them using the Geocoder::Calculations.distance_between method. This will produce accurate results but will be very slow (and use a lot of memory) if you have a lot of objects in your database.

  3. If you have a large number of objects (so you can't use approach #2) and you need accurate results (better than approach #1 will give), you can use a combination of the two. Get all the objects within a square around your center point, and then eliminate the ones that are too far away using Geocoder::Calculations.distance_between.

Because Geocoder needs to provide this functionality as a scope, we must go with option #1, but feel free to implement #2 or #3 if you need more accuracy.

Tests

Geocoder comes with a test suite (just run rake test) that mocks ActiveRecord and is focused on testing the aspects of Geocoder that do not involve executing database queries. Geocoder uses many database engine-specific queries which must be tested against all supported databases (SQLite, MySQL, etc). Ideally this involves creating a full, working Rails application, and that seems beyond the scope of the included test suite. As such, I have created a separate repository which includes a full-blown Rails application and some utilities for easily running tests against multiple environments:

http://github.com/alexreisner/geocoder_test

Error Handling

By default Geocoder will rescue any exceptions raised by calls to a geocoding service and return an empty array (using warn() to inform you of the error). You can override this on a per-exception basis, and also have Geocoder raise its own exceptions for certain events (eg: API quota exceeded) by using the :always_raise option:

Geocoder.configure(:always_raise => [SocketError, TimeoutError])

You can also do this to raise all exceptions:

Geocoder.configure(:always_raise => :all)

The raise-able exceptions are:

SocketError
TimeoutError
Geocoder::OverQueryLimitError
Geocoder::RequestDenied
Geocoder::InvalidRequest
Geocoder::InvalidApiKey

Note that not all lookups support all exceptions.

Troubleshooting

Mongoid

If you get one of these errors:

uninitialized constant Geocoder::Model::Mongoid
uninitialized constant Geocoder::Model::Mongoid::Mongo

you should check your Gemfile to make sure the Mongoid gem is listed before Geocoder. If Mongoid isn't loaded when Geocoder is initialized, Geocoder will not load support for Mongoid.

ActiveRecord

A lot of debugging time can be saved by understanding how Geocoder works with ActiveRecord. When you use the near scope or the nearbys method of a geocoded object, Geocoder creates an ActiveModel::Relation object which adds some attributes (eg: distance, bearing) to the SELECT clause. It also adds a condition to the WHERE clause to check that distance is within the given radius. Because the SELECT clause is modified, anything else that modifies the SELECT clause may produce strange results, for example:

Unexpected Responses from Geocoding Services

Take a look at the server's raw JSON response. You can do this by getting the request URL in an app console:

Geocoder::Lookup.get(:google).query_url(Geocoder::Query.new("..."))

Replace :google with the lookup you are using and replace ... with the address you are trying to geocode. Then visit the returned URL in your web browser. Often the API will return an error message that helps you resolve the problem. If, after reading the raw response, you believe there is a problem with Geocoder, please post an issue and include both the URL and raw response body.

Reporting Issues

When reporting an issue, please list the version of Geocoder you are using and any relevant information about your application (Rails version, database type and version, etc). Also avoid vague language like "it doesn't work." Please describe as specifically as you can what behavior your are actually seeing (eg: an error message? a nil return value?).

Known Issue

You cannot use the near scope with another scope that provides an includes option because the SELECT clause generated by near will overwrite it (or vice versa).

Instead of using includes to reduce the number of database queries, try using joins with either the :select option or a call to preload. For example:

# Pass a :select option to the near scope to get the columns you want.
# Instead of City.near(...).includes(:venues), try:
City.near("Omaha, NE", 20, :select => "cities.*, venues.*").joins(:venues)

# This preload call will normally trigger two queries regardless of the
# number of results; one query on hotels, and one query on administrators.
# Instead of Hotel.near(...).includes(:administrator), try:
Hotel.near("London, UK", 50).joins(:administrator).preload(:administrator)

If anyone has a more elegant solution to this problem I am very interested in seeing it.

Contributing

Contributions are welcome via pull requests on Github. Please respect the following guidelines:

Copyright (c) 2009-12 Alex Reisner, released under the MIT license