Seeking best practise advise

I am doing this app, account - project - category orientated. Category
can belong to an account (url: account.example.com/categories) or
specific to a project (url: account.example.com/projects/1/
categories), my question is:
1. is this url structure the proper way to do it?
2. inside the category controller, to determine whether the category
belong to an account or a project, i use "if param['project_id']",
again is this the proper way to do it?

Appreciate any help,

Regards,

johnny

You may find reading this helpful.

http://darynholmes.wordpress.com/2008/03/15/beginners-tutorial-routing-in-rails-20-with-rest-part-1-of-n/