How do I make a hair particle system with an object, and stop the objects overlapping

Support Particles and Physics Simulations
1

I want to make a particle system with circles and hairs but they’re all overlapping; how do I stop that happening?

Thanks

2

Checkout this Blender Guru tutorial on making a city. The buildings are actually hair. Andrew explains how to align the buildings so they do not collide with each other.
http://www.blenderguru.com/videos/how-to-create-a-city/