The 7th Permaculture principle is to "Design from Patterns to Details" (blogs on the the first 6 principles can be found here).

In order to design from patterns to details presupposes that we have some awareness of what patterns are useful to follow.

Where can we find patterns to follow? Nature comes to the rescue again.

To find patterns in nature requires us to think about the scale of space and time we are observing. Are we using a microscope and looking at soil microbiology, binoculars looking at landscape formations, or telescopes looking at the stars. Some patterns have the unusual property that they re-occur at multiple scales - simple geometric shapes, spirals, branching patterns, crennelated and lobular surfaces, cracked surfaces, and fractal surfaces are some examples.

The recurring patterns tell us something interesting about how nature handles the flow of matter and energy.

A spiral is the shape of our galaxy, it is the shape of a Rams horn and a Nautalis sea shell, and it is the shape of our DNA strands. Because it occurs at multiple scales we can consider this an interesting pattern worth investigating and understanding in more detail and perhaps incorporating into a design.

One matter and energy problem that a spiral form solves is packing alot of surface into a small area. This can be illustrated with a spiral herb garden that gives you alot of planting surface in a small area.

If you unroll the spiral it might be 40 feet long. A spiral herb garden allows you to travel to all planting surfaces much more easily than if the surface was a 40 foot long linear row of herb plantings. You can pack 40 feet of herb plantings by your front door so you have easy access to your cooking herbs. Because the spiral has a shadier and sunnier side, hotter sides and cooler sides, and moister areas at the bottom and dryer areas at the top, it also provides a variety of different microclimates for growing different types of herbs.

So one way to interpret the "Design from Patterns to Details" is as advice to study some of natures recurring patterns and find ways to incorporate them into your designs.

At a more mundane level, this principle is about looking for the big picture and letting that bigger-picture guide your actions. It is the first principle that starts to direct us towards a more wholistic view of the situation rather than a reductionist view. One way to achieve a more "wholistic" view is to look for and design based on patterns. The next 5 principles will give us other directives that orient us towards a wholistic understanding. The development of pattern understanding can help us to design from patterns to details.

In Permaculture: A Designers Manual, Bill dedicates chapter 4 to the topic Pattern Understanding. One of the ideas he discusses in this chapter is the "General Core Model". This is a difficult concept for most people to grasp and I include myself in that assessment. The general core model looks alot like a tree shape and by tweaking different parameters of the general model (e.g., number of branches, order of branching, branch angle, branch curvature, etc...) you can generate a variety of commonly occurring patterns found in nature (by taking various types of slices through the tree and observing the surface patterns under the slice). The diagram below is the main explanation given of what the General Core Model for pattern understanding is:

The tree form above (branches,trunk and roots) is the general model and by tweaking various parameters and slicing through the model, we can expose a variety of patterns commonly found in nature. That, I think is what the general model is about. You can see expressions of the tree model in a blade of grass, a shrub, a tree, a mushroom and most of the plant world. Many of these patterns are also found in water flows, air flows, desert sand accumulations, and elsewhere.

Some fractals are tree-like in appearance. Some of the recent developments in fractal animation software makes me think fractals might be a better candidate for the general model or else might provide the implementation details of Mollison's general tree model.

Here is a concluding quote from Bill's chapter on Pattern Understanding:

Learning to master a pattern is very like learning a principle; it may be applicable over a wide range of phenomena, some complex and some simple.