Organizing source code is a key component to easily understanding it. Shawn McCool inspired me to reorganize a php project I have been working on. He created a very fun talk that covers this among other great points. Around minute 10:22 Shawn brings up the concept of Namespacing by Type.

The goal is simple. You place the objects that are related to each other in the same namespace. This organizes the related files together into the same folder. It also reduces the number of use Namespaced\Object; statements at the top of your php classes.