Card sorting is a technique for figuring out how users think about what goes with what so you can organize information on your website in a way that feels intuitive and makes sense. It's particularly useful for designing menus and other navigation systems.
A course instructor wanted to know how best to set up the menus on the course website. Each of the students was given a stack of cards, one card for each page of the site, and asked to organize them into groups, as shown below.
Not surprisingly, the students didn't all agree, so we used a statistical technique called hierarchical agglomerative clustering to identify groupings that reflected what an "average" student thought.
This was used to construct a site map showing how the site navigation should be set up: