Geokit Plugin: Geocoder, Distance Finders, and more


Geokit consists of a Gem ([geokit-gem]( and a Rails plugin ([geokit-rails](

#### 1. Install the Rails plugin:

    script/plugin install git://

#### 2. Add this line to your environment.rb (inside the do |config| block)

                config.gem "geokit"

This informs Rails of the gem dependency.

#### 3. Tell Rails to install the gem:

                rake gems:install

And you’re good to go! If you’re running an older verion of Rails, just install the gem manually: `sudo gem install rails`


Geokit provides key functionality for location-oriented Rails applications:

The goal of this plugin is to provide the common functionality for location-oriented applications (geocoding, location lookup, distance calculation) in an easy-to-use package.


Throughout the code and API, latitude and longitude are referred to as lat and lng. We’ve found over the long term the abbreviation saves lots of typing time.


To get started, just specify an ActiveRecord class as `acts_as_mappale`:

    class Location < ActiveRecord::Base

There are some defaults you can override:

    class Location < ActiveRecord::Base
      acts_as_mappable :default_units => :miles,
                       :default_formula => :sphere,
                       :distance_field_name => :distance,
                       :lat_column_name => :lat,
                       :lng_column_name => :lng

The optional parameters are :units, :formula, and distance_field_name. Values for :units can be :miles, :kms (kilometers), or :nms (nautical miles), with :miles as the default. Values for :formula can be :sphere or :flat with :sphere as the default. :sphere gives you Haversine calculations, while :flat gives the Pythagoreum Theory. These defaults persist through out the plug-in.

The plug-in creates a calculated `distance` field on AR instances that have been retrieved throw a Geokit location query. By default, these fields are known as “distance” but this can be changed through the `:distance_field_name` key.

You can also define alternative column names for latitude and longitude using the `:lat_column_name` and `:lng_column_name` keys. The defaults are ‘lat’ and ‘lng’ respectively.

Once you’ve specified acts_as_mappable, a set of distance-based finder methods are available:

Origin as a two-element array of latititude/longitude:

                find(:all, :origin => [37.792,-122.393])

Origin as a geocodeable string:

                find(:all, :origin => '100 Spear st, San Francisco, CA')

Origin as an object which responds to lat and lng methods, or latitude and longitude methods, or whatever methods you have specified for `lng_column_name` and `lat_column_name`:

                find(:all, :origin=>my_store) # and my_store.lng methods exist

Often you will need to find within a certain distance. The prefered syntax is:

    find(:all, :origin => @somewhere, :within => 5)

. . . however these syntaxes will also work:

    find_within(5, :origin => @somewhere)
    find(:all, :origin => @somewhere, :conditions => "distance < 5")

Note however that the third form should be avoided. With either of the first two, Geokit automatically adds a bounding box to speed up the radial query in the database. With the third form, it does not.

If you need to combine distance conditions with other conditions, you should do so like this:

    find(:all, :origin => @somewhere, :within => 5, :conditions=>['state=?',state])

If :origin is not provided in the finder call, the find method works as normal. Further, the key is removed from the :options hash prior to invoking the superclass behavior.

Other convenience methods work intuitively and are as follows:

    find_within(distance, :origin => @somewhere)
    find_beyond(distance, :origin => @somewhere)
    find_closest(:origin => @somewhere)
    find_farthest(:origin => @somewhere)

where the options respect the defaults, but can be overridden if desired.

Lastly, if all that is desired is the raw SQL for distance calculations, you can use the following:

    distance_sql(origin, units=default_units, formula=default_formula)

Thereafter, you are free to use it in find_by_sql as you wish.

There are methods available to enable you to get the count based upon the find condition that you have provided. These all work similarly to the finders. So for instance:

    count(:origin, :conditions => "distance < 5")
    count_within(distance, :origin => @somewhere)
    count_beyond(distance, :origin => @somewhere)


If you are displaying points on a map, you probably need to query for whatever falls within the rectangular bounds of the map:

    Store.find :all, :bounds=>[sw_point,ne_point]

The input to :bounds can be array with the two points or a Bounds object. However you provide them, the order should always be the southwest corner, northeast corner of the rectangle. Typically, you will be getting the sw_point and ne_point from a map that is displayed on a web page.

If you need to calculate the bounding box from a point and radius, you can do that:

    Store.find :all, :bounds=>bounds


You can use includes along with your distance finders:

    stores=Store.find :all, :origin=>home, :include=>[:reviews,:cities] :within=>5, :order=>'distance'

However, ActiveRecord drops the calculated distance column when you use include. So, if you need to use the distance column, you’ll have to re-calculate it post-query in Ruby:


In this case, you may want to just use the bounding box condition alone in your SQL (there’s no use calculating the distance twice):

    stores=Store.find :all, :include=>[:reviews,:cities] :bounds=>bounds

## USING :through

You can also specify a model as mappable “through” another associated model. In other words, that associated model is the actual mappable model with “lat” and “lng” attributes, but this “through” model can still utilize all of the above find methods to search for records.

    class Location < ActiveRecord::Base
      belongs_to :locatable, :polymorphic => true

    class Company < ActiveRecord::Base
      has_one :location, :as => :locatable  # also works for belongs_to associations
      acts_as_mappable :through => :location

Then you can still call:

    Company.find_within(distance, :origin => @somewhere)

You can also give :through a hash if you location is nested deep. For example, given:

    class House

    class Family
      belongs_to :house

    class Person
      belongs_to :family
      acts_as_mappable :through => { :family => :house }

Remember that the notes above about USING INCLUDES apply to the results from this find, since an include is automatically used.


You can obtain the location for an IP at any time using the geocoder as in the following example:

    location = IpGeocoder.geocode('')

where Location is a GeoLoc instance containing the latitude, longitude, city, state, and country code. Also, the success value is true.

If the IP cannot be geocoded, a GeoLoc instance is returned with a success value of false.

It should be noted that the IP address needs to be visible to the Rails application. In other words, you need to ensure that the requesting IP address is forwarded by any front-end servers that are out in front of the Rails app. Otherwise, the IP will always be that of the front-end server.

The Multi-Geocoder will also geocode IP addresses and provide failover among multiple IP geocoders. Just pass in an IP address for the parameter instead of a street address. Eg:

        location = Geocoders::MultiGeocoder.geocode('')

The MultiGeocoder class requires 2 configuration setting for the provider order. Ordering is done through `Geokit::Geocoders::provider_order` and `Geokit::Geocoders::ip_provider_order`, found in `config/initializers/geokit_config.rb`. If you don’t already have a `geokit_config.rb` file, the plugin creates one when it is first installed.


A class method called geocode_ip_address has been mixed into the ActionController::Base. This enables before_filter style lookup of the IP address. Since it is a filter, it can accept any of the available filter options.

Usage is as below:

    class LocationAwareController < ActionController::Base

A first-time lookup will result in the GeoLoc class being stored in the session as `:geo_location` as well as in a cookie called `:geo_session`. Subsequent lookups will use the session value if it exists or the cookie value if it doesn’t exist. The last resort is to make a call to the web service. Clients are free to manage the cookie as they wish.

The intent of this feature is to be able to provide a good guess as to a new visitor’s location.


Geocoding has been integrated with the finders enabling you to pass a physical address or an IP address. This would look the following:

    Location.find_farthest(:origin => '')
    Location.find_farthest(:origin => 'Irving, TX')

where the IP or physical address would be geocoded to a location and then the resulting latitude and longitude coordinates would be used in the find. This is not expected to be common usage, but it can be done nevertheless.


Geocoding is provided by the Geokit gem, which is required for this plugin. See the top of this file for instructions on installing the Geokit gem.

Geokit can geocode addresses using multiple geocodeing web services. Geokit supports services like Google, Yahoo, and, and more — see the Geokit gem API for a complete list.

These geocoder services are made available through the following classes: GoogleGeocoder, YahooGeocoder, UsGeocoder, CaGeocoder, and GeonamesGeocoder. Further, an additional geocoder class called MultiGeocoder incorporates an ordered failover sequence to increase the probability of successful geocoding.

All classes are called using the following signature:

    include Geokit::Geocoders
    location = XxxGeocoder.geocode(address)

where you replace Xxx Geocoder with the appropriate class. A GeoLoc instance is the result of the call. This class has a “success” attribute which will be true if a successful geocoding occurred. If successful, the lat and lng properties will be populated.

Geocoders are named with the convention NameGeocoder. This naming convention enables Geocoder to auto-detect its sub-classes in order to create methods called `name_geocoder(address)` so that all geocoders can be called through the base class. This is done purely for convenience; the individual geocoder classes are expected to be used independently.

The MultiGeocoder class requires the configuration of a provider order which dictates what order to use the various geocoders. Ordering is done through `Geokit::Geocoders::provider_order`, found in `config/initializers/geokit_config.rb`.

If you don’t already have a `geokit_config.rb` file, the plugin creates one when it is first installed.

Make sure your failover configuration matches the usage characteristics of your application — for example, if you routinely get bogus input to geocode, your code will be much slower if you have to failover among multiple geocoders before determining that the input was in fact bogus.

The Geocoder.geocode method returns a GeoLoc object. Basic usage:

    loc=Geocoder.geocode('100 Spear St, San Francisco, CA')
    if loc.success
      puts loc.lng
      puts loc.full_address


Currently, only the Google Geocoder supports reverse geocoding. Pass the lat/lng as a string, array or LatLng instance:

                res=Geokit::Geocoders::GoogleGeocoder.reverse_geocode "37.791821,-122.394679"
                => #<Geokit::GeoLoc:0x558ed0 ...
                "101-115 Main St, San Francisco, CA 94105, USA"

The address will usually appear as a range, as it does in the above example.


Just has you can pass an IP address directly into an ActiveRecord finder as the origin, you can also pass a physical address as the origin:

    Location.find_closest(:origin => '100 Spear st, San Francisco, CA')

where the physical address would be geocoded to a location and then the resulting latitude and longitude coordinates would be used in the find.

Note that if the address fails to geocode, the find method will raise an ActiveRecord::GeocodeError you must be prepared to catch. Alternatively, You can geocoder the address beforehand, and pass the resulting lat/lng into the finder if successful.

## Auto Geocoding

If your geocoding needs are simple, you can tell your model to automatically geocode itself on create:

    class Store < ActiveRecord::Base
      acts_as_mappable :auto_geocode=>true

It takes two optional params:

    class Store < ActiveRecord::Base
      acts_as_mappable :auto_geocode=>{:field=>:address, :error_message=>'Could not geocode address'}

. . . which is equivilent to:

    class Store << ActiveRecord::Base
      before_validation_on_create :geocode_address

      def geocode_address
        geo=Geokit::Geocoders::MultiGeocoder.geocode (address)
        errors.add(:address, "Could not Geocode address") if !geo.success, self.lng =,geo.lng if geo.success

If you need any more complicated geocoding behavior for your model, you should roll your own `before_validate` callback.

## Distances, headings, endpoints, and midpoints

    distance=home.distance_from(work, :units=>:miles)
    heading=home.heading_to(work) # result is in degrees, 0 is north
    endpoint=home.endpoint(90,2)  # two miles due east

## Cool stuff you can do with bounds,ne_point)

HOW TO . . .


A few quick examples to get you started .…

## How to install the Geokit Rails plugin (See the very top of this file)

## How to find all stores within a 10-mile radius of a given lat/lng

  1. ensure your stores table has lat and lng columns with numeric or float datatypes to store your latitude/longitude
  2. use `acts_as_mappable` on your store model:
     class Store < ActiveRecord::Base
  3. finders now have extra capabilities:
     Store.find(:all, :origin =>[32.951613,-96.958444], :within=>10)

## How to geocode an address

  1. configure your geocoder key(s) in `config/initializers/geokit_config.rb`
  2. also in `geokit_config.rb`, make sure that `Geokit::Geocoders::provider_order` reflects the geocoder(s). If you only want to use one geocoder, there should be only one symbol in the array. For example:
  3. Test it out in script/console
     include Geokit::Geocoders
     res = MultiGeocoder.geocode('100 Spear St, San Francisco, CA')
     puts res.lng
     puts res.full_address
     ... etc. The return type is GeoLoc, see the API for
     all the methods you can call on it.

## How to find all stores within 10 miles of a given address

  1. as above, ensure your table has the lat/lng columns, and you’ve applied `acts_as_mappable` to the Store model.
  2. configure and test out your geocoder, as above
  3. pass the address in under the :origin key
                 Store.find(:all, :origin=>'100 Spear st, San Francisco, CA',
  4. you can also use a zipcode, or anything else that’s geocodable:
                 Store.find(:all, :origin=>'94117',

## How to sort a query by distance from an origin

You now have access to a ‘distance’ column, and you can use it as you would any other column. For example:

                Store.find(:all, :origin=>'94117', :order=>'distance')

## How to elements of an array according to distance from a common point

Usually, you can do your sorting in the database as part of your find call. If you need to sort things post-query, you can do so:

    stores=Store.find :all
    puts stores.first.distance

Obviously, each of the items in the array must have a latitude/longitude so they can be sorted by distance.

## Database indexes

MySQL can’t create indexes on a calculated field such as those Geokit uses to calculate distance based on latitude/longitude values for a record. However, indexing the lat and lng columns does improve Geokit distance calculation performance since the lat and lng columns are used in a straight comparison for distance calculation. Assuming a Page model that is incorporating the Geokit plugin the migration would be as follows.

    class AddIndexOPageLatAndLng < ActiveRecord::Migration

      def self.up
        add_index  :pages, [:lat, :lng]

      def self.down
        remove_index  :pages, [:lat, :lng]

## Database Compatability


`acts_as_mappable.rb`, as you’d expect, contains the ActsAsMappable module which gets mixed into your models to provide the location-based finder goodness.

`ip_geocode_lookup.rb` contains the before_filter helper method which enables auto lookup of the requesting IP address.

### The Geokit gem provides the building blocks of distance-based operations:

The Mappable module, which provides basic distance calculation methods, i.e., calculating the distance between two points.

The LatLng class is a simple container for latitude and longitude, but it’s made more powerful by mixing in the above-mentioned Mappable module — therefore, you can calculate easily the distance between two LatLng ojbects with `distance = first.distance_to(other)`

GeoLoc represents an address or location which has been geocoded. You can get the city, zipcode, street address, etc. from a GeoLoc object. GeoLoc extends LatLng, so you also get lat/lng AND the Mappable modeule goodness for free.


Follow the Google Group for updates and discussion on Geokit:


*1. The configuration file*: Geokit for Rails uses a configuration file in config/initializers. You must add your own keys for the various geocoding services if you want to use geocoding. If you need to refer to the original template again, see the `assets/api_keys_template` file.

*2. The gem dependency*: Geokit for Rails depends on the Geokit gem. Tell Rails about this dependency in `config/environment.rb`, within the initializer block: config.gem “geokit“

*If you’re having trouble with dependencies .…*

Try installing the gem manually (sudo gem install geokit), then adding a `require ‘geokit’` to the top of `vendor/plugins/geokit-rails/init.rb` and/or `config/geokit_config.rb`.





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