[*Rails*] 指定座標のGoogleMapを表示させたい ref: http://qiita.com/cigalecigales/items/bfdaa07a7fa29a4175cb

application.js

(省略)...
//= require jquery
//= require jquery_ujs
//= require turbolinks
//= require underscore
//= require gmaps/google
//= require_tree .

cicada.rb

class Cicada < ActiveRecord::Base
    reverse_geocoded_by :latitude, :longitude
    after_validation :geocode
end

file1.txt

$ bundle install

file10.txt

$ rails c
irb(main):001:0> Cicada.create(title: "abura", address: "kobe station")
=> #<Cicada id: 13, title: "abura", description: nil, address: "kobe station", latitude: 34.679526, longitude: 135.178021, created_at: "2015-02-22 05:11:26", updated_at: "2015-02-22 05:11:26">

file11.txt

irb(main):001:0> Cicada.create(title: "abura", address: "tokyo station", latitude:10, longitude:140)
=> #<Cicada id: 15, title: "abura", description: nil, address: "tokyo station", latitude: 35.681382, longitude: 139.766084, created_at: "2015-02-22 05:14:58", updated_at: "2015-02-22 05:14:58">

file13.txt

irb(main):001:0> Cicada.create(title: "abura", address: "tokyo station", latitude:36.091521, longitude:139.372694)
=> #<Cicada id: 17, title: "abura", description: nil, address: "tokyo station", latitude: 36.091521, longitude: 139.372694, created_at: "2015-02-22 05:23:54", updated_at: "2015-02-22 05:23:54">

file2.txt

$ rails g model Cicada title:string description:string address:string latitude:float longitude:float
$ rake db:migrate

file4.txt

$ rails g controller map index

Gemfile

(省略)...
# Google map
gem 'gmaps4rails'
48 gem 'geocoder'

index.html.erb

<script src="//maps.google.com/maps/api/js?v=3.13&amp;sensor=false&amp;libraries=geometry" type="text/javascript"></script>
<script src='//google-maps-utility-library-v3.googlecode.com/svn/tags/markerclustererplus/2.0.14/src/markerclusterer_packed.js' type='text/javascript'></script>

<div style='width: 800px;'>
  <div id="map" style='width: 800px; height: 400px;'></div>
</div>

<script type="text/javascript">
    handler = Gmaps.build('Google');
    handler.buildMap({ provider: {}, internal: {id: 'map'}}, function(){
      markers = handler.addMarkers(<%=raw @hash.to_json %>);
      handler.bounds.extendWith(markers);
      handler.fitMapToBounds();
    });
</script>

map_controller.rb

class MapController < ApplicationController
  def index
        @cicadas = Cicada.all
        @hash = Gmaps4rails.build_markers(@cicadas) do |cicada, marker|
            marker.lat cicada.latitude
            marker.lng cicada.longitude
            marker.infowindow cicada.description
            marker.json({ title: cicada.title })
        end
  end
end

routes.rb

Rails.application.routes.draw do
  root 'map#index'
  (省略)...
end

underscore.js

  //(underscore.jsまたはunderscore-min.jsの中身を貼り付ける。)