Create Your Own Geodatabase using Ruby on Rails and Google Maps

Posted by Lars | Posted in Geocoding, Rails, Ruby, Tutorials | Posted on 04-05-2009

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Geocoding with Ruby on Rails isn’t a big deal. But sometimes you have do more than simple geocoding. For real estate webpages you need information about state, county or suburb for a given address.

This tutorial will show you how to build your own geodatabase without overusing google maps requests(limited on 15000 Requests per Ip/month).

Before you can start you must have a fresh rails application and a google maps api key. You can signup for one here: http://code.google.com/apis/maps/

This tutorial has following parts:

Geocode an address
Get extented information to this address
An Pratical example

We touch only the model layer(thin controllers fat models). I will use an address ressource like follows:

script/generate scaffold Address country:string state:string 

county:string city:string suburb:string zipcode:string street:string 

streetno:string longitude:float latitude:float error_code:string

and

rake db:migrate

You can use this address ressources for many purposes. But more on this later. You need some ruby-gems too.

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class Address < ActiveRecord::Base

  require 'open-uri'

  require 'cgi'

  require 'hpricot'

  require 'iconv'

  ...

end

Geocode an address

For geocoding an address you can use a simple callback function.

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def before_create

  geocode

end

And the gecode function itself:

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def geocode

  url = ["http://maps.google.com/maps/geo?q="]

  url << address_for_geocoding

  url << "&output=xml&key="

  url << "your_google_maps_api_key"

    open(url.to_s) do |file|

      @body = file.read

      doc = Hpricot(@body)

      (doc/:status/:code).each do |code|

        self.error_code = code.inner_html

      end

      (doc/:point/:coordinates).each do |link|

        self.longitude, self.latitude = link.inner_html.split(',')

      end    

    end  

end

On line 3 i need an encoded address for proper geocoding. This function catches incomplete address information too.

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def address_for_geocoding

  addressline = []      

  addressline << streetno.to_i unless (streetno || "").blank?

  addressline << street unless (street || "").blank?

  addressline << zipcode unless (zipcode || "").blank?

  addressline << city unless (city || "").blank?        

  CGI::escape(addressline.join(' '))

end

On line 8 we start the parsing of the returned xml-data from google maps. For more information about the xml structure you can read: Google Maps XML Structure

On line 15 we assign the longitude and latitude to our address attributes. So you get the coordinates into address model before rails creates it.

Get extented information

You can read at Google Maps XML Structure that far more information can delivered from google maps. So we update our geocode function:

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def geocode

  url = ["http://maps.google.com/maps/geo?q="]

  url << address_for_geocoding

  url << "&output=xml&key="

  url << "your_google_maps_api_key"

    open(url.to_s) do |file|

      @body = file.read

      doc = Hpricot(@body)

      (doc/:status/:code).each do |code|

        self.error_code = code.inner_html

      end

      (doc/:country/:countrynamecode).each do |country_code|

        self.country = country_code.inner_html

      end

      (doc/:country/:administrativearea/:administrativeareaname).each do |area|

        self.state = Iconv.conv('utf-8', 'ISO-8859-1', area.inner_html)

      end

      (doc/:country/:administrativearea/:subadministrativearea/:subadministrativeareaname).each do |sub_area|

        self.county = Iconv.conv('utf-8', 'ISO-8859-1', sub_area.inner_html)

      end

      (doc/:country/:administrativearea/:subadministrativearea/:locality/:dependentlocality/:dependentlocalityname).each do |t_area|

        self.suburb = Iconv.conv('utf-8', 'ISO-8859-1', t_area.inner_html)

      end 

      (doc/:point/:coordinates).each do |link|

        self.longitude, self.latitude = link.inner_html.split(',')

      end    

    end  

end

So we get extented information about country, state, county and suburb related to the address information you entered. You have now the complete set of address, administrative-level information and geo coordinates.

A practical example

It’s time for some practical stuff. I will use real estate example. In this example i will geocode a house location and add administrative information to it.

So let’s start with a property ressource scaffold:

script/generate scaffold Property title:string description:text 

street:string streetno:string zip:string city:string address_id:integer

and

rake db:migrate

I know there are some redundant address information, but it’s necessary to trace typing errors from users.

Lets go to the model layer an make some associations. One house can only have one address but one address can have many houses. So we write:

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class Address < ActiveRecord::Base

  has_many :properties

  ...

end

and

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class Property < ActiveRecord::Base

  belongs_to :address

  ...

end

Now lets start coding:

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class Property < ActiveRecord::Base

  belongs_to :address

  after_save :get_location

  protected  

  def get_location

    address = address_exist?

    address =Address.create(:streetno =>self.streetno, 

     :street => self.street,:zip => self.zip, 

     :city => self.city) unless address

    self.address = address

  end

  def address_exist?

    address = Address.find(:first,

    :conditions => "streetno = ? and street= ? 

    and zip = ? and city = ?",

    self.streetno,self.street,self.zip,self.city)

    address ? address : false

  end

end

Done. What happened? If you enter property data the property will saved. After save we call the get_location function to assign a address to our new property.

On line 7 we call the address_exist? function which try to find an address in our database. If this address doesn’t exist we create a new one on line 8.

Everytime a user adds unknown property your address database will grow. Once an address is saved it will resused every time a property with same address is entered.

Now you can get property listings like:

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class Property < ActiveRecord::Base

  belongs_to :address

  ...

  def get_all_properties_with_same_streetname

    addresses = Address.find(:all,

    :conditions => ["street = ?",self.street])

    addresses.collect { |address| address.properties }

  end

  ...

end

I hope i could help you with this tutorial. Please write a comment if you have any questions or critics.

Comments (6)

MartOn said on 06-05-2009
	Nice tutorial. I am looking for a tutorial for generating tracks from GPX files and showing them using google maps in ruby on Rails. Any1 who know how to do this in a simple way? /MartOn

Lars said on 06-05-2009
	Hi marton, thanks for your comment. In one of my next tutorials i will explain how to import data from xml files into rails applications. It isn’t exactly the same but i am sure you can solve your problem with it. See you later, Lars

Bart said on 25-05-2009
	Thanks for the tuturial! It works here! Only you must change this addressline << zip unless (zip \|\| “”).blank? into addressline << zipcode unless (zipcode \|\| “”).blank? If i do that it works otherwise it gives an error

Lars said on 25-05-2009
	Thank you bart, i fixed the error in tutorial. Kind regards, Lars

KrisBelucci said on 02-06-2009
	da best. Keep it going! Thank you

Jared said on 01-10-2009
	Hey, I really dig the article, very helpful. Maybe you can help with the next part, I’m looking to parse an address from a block of text (think Craigslist). Any idea how one would go about that? Seems like some serious regex.

larsgebhardt

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