How to setup PostGIS with Rails

create_locations.rb

class CreateLocations < ActiveRecord::Migration
  def self.up
    create_table :locations do |t|
      t.datetime :time
      t.point :geom, :null => false, :srid => 4326, :with_z => true
      t.float :speed
    end
  end

  def self.down
    drop_table :locations
  end
end

postgis - create template.txt

http://www.lincolnritter.com/blog/2007/12/04/installing-postgresql-postgis-and-more-on-os-x-leopard/

Connect to the template database
$ psql template1

Execute the following commands:
template1=# create database template_postgis with template = template1;
template1=# UPDATE pg_database SET datistemplate = TRUE where datname = 'template_postgis';

Connect to the new template_postgis database:
template1=# \c template_postgis

Add PostGIS extensions and grant access to everyone to spatial tables:
template_postgis=# CREATE LANGUAGE plpgsql;
template_postgis=# \i /opt/local/share/postgresql84/contrib/postgis-1.5/postgis.sql;
template_postgis=# \i /opt/local/share/postgresql84/contrib/postgis-1.5/spatial_ref_sys.sql;
template_postgis=# GRANT ALL ON geometry_columns TO PUBLIC;
template_postgis=# GRANT ALL ON spatial_ref_sys TO PUBLIC;

Prevent further modifications to the template_postgis database:
template_postgis=# VACUUM FREEZE;

postgis - database.yml

common: &common
  adapter: postgresql
  host: localhost
  port: 5432
  username:
  password:
  encoding: utf8
  template: template_postgis
  pool: 5
  timeout: 5000

development:
  <<: *common
  database: development

# Warning: The database defined as "test" will be erased and
# re-generated from your development database when you run "rake".
# Do not set this db to the same as development or production.
test:
  <<: *common
  database: test

production:
  <<: *common
  database: production