routeのmoduleとnamespaceとscopeの違い ref: http://qiita.com/blueplanet/items/522cc8364f6cf189ecad

file0.rb

namespace :admin do
  resources :users
end

# rake routes
        Prefix Verb   URI Pattern                     Controller#Action
   admin_users GET    /admin/users(.:format)          admin/users#index
               POST   /admin/users(.:format)          admin/users#create
new_admin_user GET    /admin/users/new(.:format)      admin/users#new
dit_admin_user GET    /admin/users/:id/edit(.:format) admin/users#edit
    admin_user GET    /admin/users/:id(.:format)      admin/users#show
               PATCH  /admin/users/:id(.:format)      admin/users#update
               PUT    /admin/users/:id(.:format)      admin/users#update
               DELETE /admin/users/:id(.:format)      admin/users#destroy

file1.rb

scope module: :admin do
  resources :users
end

# rake routes
   Prefix Verb   URI Pattern               Controller#Action
    users GET    /users(.:format)          admin/users#index
          POST   /users(.:format)          admin/users#create
 new_user GET    /users/new(.:format)      admin/users#new
edit_user GET    /users/:id/edit(.:format) admin/users#edit
     user GET    /users/:id(.:format)      admin/users#show
          PATCH  /users/:id(.:format)      admin/users#update
          PUT    /users/:id(.:format)      admin/users#update
          DELETE /users/:id(.:format)      admin/users#destroy

file2.rb

scope '/admin' do
  resources :users
end

# rake routes
   Prefix Verb   URI Pattern                     Controller#Action
    users GET    /admin/users(.:format)          users#index
          POST   /admin/users(.:format)          users#create
 new_user GET    /admin/users/new(.:format)      users#new
edit_user GET    /admin/users/:id/edit(.:format) users#edit
     user GET    /admin/users/:id(.:format)      users#show
          PATCH  /admin/users/:id(.:format)      users#update
          PUT    /admin/users/:id(.:format)      users#update
          DELETE /admin/users/:id(.:format)      users#destroy