Display a Google Map with Rails

In my last article on geopositioning with Rails and Google maps, we saw how to use the YM4R/GM plugin to find and store the longitude/latitude of an address using the Google Maps api. With these informations, we can now display the map to the user. We’ll see how to do this in three easy steps.

1. Prepare the map in your model

In your Geolocation model, start by adding this snippet of code which will initialize your map.

def map
  @map ||= prepare_map
end

def mapped?
  latitude && longitude
end

def coordinates
  [latitude, longitude]
end

private

def prepare_map
  return unless mapped?
  returning GMap.new("gmap") do |map| 
    map.control_init(:large_map => true, :map_type => true)
    map.center_zoom_init(coordinates, 15) # Set the center and zoo level
    map.overlay_init(GMarker.new(coordinates))
  end
end

The important method here is prepare_map. What it does is create a new map centered at the given coordinates. The overlay_init method sets a marker at the coordinates position. This is a basic vanilla map initialization. You might want to read the YM4R api for more options like adding an info window or multiple markers.

2. Call it from your controller

In our controller, we will set the @map variable to make it accessible in our view :

@map = customer.geolocation.map

3. Display the map in your view

You will need this snippet of code in the header section of your document to do the proper javascript imports and initializations :

= GMap.header
= @map.to_html

And in the body of your view, where you want to display the map, simply add :

@map.div(:width => 600, :height => 400)

This last line will generate a div with the id “gmap” (or whatever name you set in the GMap.new function). I find it’s cleaner to just set the width an height through CSS.

4. Adding complexity

This technique will only work if you display only one map on the page. The map needs to be visible on page load to be properly displayed. But what if there is multiple maps you want to display on the same page? And what if you want to show them in overlay popups? You probably don’t want to initialize them all on page load since it will freeze the client browser. This will require some javscript hacking. I will show you how to do that next week!

Rails geopositioning with Google Maps

A common problem when building a Rails web application that deals with addresses is geopositioning. Geopositioning can have different meaning depending on what you’re trying to achieve. In this article and the following, I will describe my solution to the following problems :

1. The user enters an address and you need to validate it and geoposition it (latitude & longitude) on a map.
2. You need to display the google map for that given address on a webpage.

Today, I will show you how I did the first step using the YM4R/GM plugin.

1- Setup the plugin and get you Google Maps key

First thing to do is to install the YM4R/GM plugin plugin. There is also a gem but it seems to be a stripped-down version of the plugin. I couldn’t get it working so I would advise to use the plugin :

script/plugin install svn://rubyforge.org/var/svn/ym4r/Plugins/GM/trunk/ym4r_gm

The plugin creates a file in your config folder named gmaps_api_key.xml. You need to enter your Google Maps API keys for the different environments. You can get the keys here.

2- Create the model

Next thing to do is to create your Geolocation activerecord model. You need to at least have those four attributes :

create_table "geolocations", :force => true do |t|
  t.string   "address"
  t.string   "city"
  t.float    "latitude"
  t.float    "longitude"
end

You might also want to add the country and postal code to the mix. But in most case, Google Maps will be able to return you a location with just a street address and a city.

3- Set the geolocation on the before_save

When you create a new gelocation record, you want to geoposition it. Here’s my code in the Geolocation.rb model :

before_save :set_geolocation

def set_geolocation
  if changes['address'] || changes['city'] || !mapped?
    results = Geocoding::get(complete_address)
    if results.status == Geocoding::GEO_SUCCESS
      self.latitude, self.longitude = results[0].latlon
    else  
      self.latitude, self.longitude = nil
    end
  end
end

def complete_address
  [address, city].select(&:present?).join(', ')
end

def mapped?
  latitude && longitude
end

What this does is set the latitude and longitude for the given address on the before_save callback. We first check if the address or the city changed and if so we try to get a geocoding. If the API responds with SUCCESS, we set the latitude and longitude with the first result. If the API failed to return a valid address, we set the latitude and longitude to nil. We can check if the address was mapped using the mapped? method.

4- Wrap it up

Geopositionning the address is only the first part of the problem. Next week I’ll show you how to use the latitude and longitude information we stored to display Google maps in your webpages.

Next week : How to display a google map for a geopositioned address

Generate RSS feeds on the fly with Feed43

Working as a freelancer, I have to monitor job boards, twitter keywords and other news channels so that I’m the first to know when someone needs a Rails developer for a contract project in Montreal or elsewhere. I manage all this information through RSS feeds with the help of Google Reader.

On some rare occasion, I stumble on a job listing site that has no support for RSS feed. This is the case for the Working With Rails job board. Apparently I’m not the only one complaining about the lack of a RSS feed for the job board.

I did some Google searches and found Feed43, a nice little web app that lets you build a RSS feed for any pages on the web. It’s free, intuitive and fairly easy to build your own RSS feed if you’re a little tech savvy. If you’re also looking for Rails gigs, feel free to use my generated WWR job board feed!