We'll begin by sketching out some of the ideas that we want to include for a college campus conceptual design. We'll use this rough sketch as a road map to refer to as we begin to draw the different elements of our concept.
Following this we'll establish our horizon line and vanish point so we can draw many of the different elements of our concept in perspective. From here we'll spend several lessons designing and drawing roads, buildings, sidewalks and other visual components that will make up our final piece.
By going through this process, you'll be able to tackle your own landscaping design concepts with more purpose and clarity while having a lot of fun.
More info - http://www.digitaltutors.com/tutorial/1350-Conceptualizing-Landscape-Designs-in-Photoshop