Casey Trees, Washington DC's primary urban forestry nonprofit, has released its Tree Space Design Report, specifically geared towards designers. Other resources for design professionals include Innovative Tree Spaces in DC, Tree Planting Detail, Interactive Maps & Tools, and Lunch and Learn.
A photograph does speak a thousand words and the report's illustrations do just that. Soil volume is really critical for healthy and long-term growth. A healthy tree can provide numerous ecological and social benefits over its lifetime.
Given the size of the tree (at maturity) and its required soil volume, there are several tree space designs: (1) Open
(3) Partially covered
Design #2 and #3 are commonly seen in downtown and commercial areas while design #1 and #2 are more common in residential areas.