I've created a diagram which allows you to quickly choose a substitute hop variety when the one in your recipe is not available.
There are many varieties of hops. Now imagine you have a beer recipe which calls for--say--Bramling Cross hops. You go to your local home brewing store and find they do not have Bramling Cross hops. How do you quickly choose a good substitution?
Tricky problems like this, in my business, often benefit from a picture or diagram. In computer science, we frequently use this great tool called GraphViz which draws graphs. (A graph is simply a bunch of circles connected by lines.). I used GraphViz to automatically draw a diagram of hop varieties. Each hop variety is a vertex (circle) in the graph. Each edge (connecting line) means that you can substitute the two hops it connects for each other.
For example, the line connecting Northern Brewer to Nugget means that you could substitute Northern Brewer hops for Nugget in a recipe, and vice versa. We plan on posting a copy of this diagram in the store, and have highlighted the hops we currently carry. This will allow us to find you a good hop for whatever recipe you might bring in.