The term Pattern Language has been applied to several different areas. Here are some.
(a) Architecture - Christopher Alexander
(b) Sustainability - Stewart Cowan
Patterns in nature serve certain functions. A branching pattern indicates distribution or collection. Explosion patterns indicate distribution. Cracks indicates expansion or compaction (function is to release energy).
When we explore and familiarize ourselves with these patterns and the functions they serve, we (a) have an idea of what function an existing pattern in nature has before exploring the particular instance in depth, and (b) can apply these patterns in our designs depending on the function they are to serve. The patterns can be applied on any scale - regional planning, cities, communities, gardens and buildings.
Sensitive dependence on initial conditions is a central idea from complexity, and specifically chaos, theories. It is also known as the butterfly effect. The terms applies to complex systems, and refer to small variations in initial conditions having large effects on the trajectory of the system. Initial choices has large effects on the final outcome.
Some examples: Deer trails becoming highways. Spacing between wheels of roman carts, becoming the standard train guage. Assyrians prison camps (straight lines, easy view and access + dividing people from each other), becoming the grid system of modern cities.