Alternatively, you could specify the column to be a serialized Array
on your model. For example:
class Model < ActiveRecord::Base
serialize :coordinates, Array
Model.create(:coordinates => [[1,2],[3,4]])
Model.find(:first, :order => 'id DESC').coordinates
In your database, you'll need to specify 'coordinates' as :text
or :string (the former preferred if you have lots of data).