Topographic materials

Hello All,

I have a substation that I'm working on and I'm going to do some renders and I noticed that I have sand, tufts of grass and two different types of gravel on site.  My question is that I have seen some really cool renders that have been done with one material.  Procedural maybe?  I'm trying to wrap my head around the best way to achieve this.  Am I using different B/W or Ambient Occlusion maps to define the characteristics of where I want the grass to grow and the sand and gravel to display?

Thanks,

J