Card Sorting
Understanding how people actually group and label things.
What It Is
A method for evaluating or designing information architecture by having users organize content into categories. How your team organizes information is probably not how your users think about it. Card sorting reveals the difference.
Open vs. Closed
Open card sorting: participants create their own categories and labels — good for discovering how users naturally group things. Closed card sorting: participants sort into predefined categories — good for validating a proposed structure.
Tree Testing
The complement to card sorting. Give users a category structure and ask them to find specific items. Measures findability without visual design influence. If people can't find things in your tree, no amount of visual design will fix that.
What It Produces
Category structures that reflect user mental models. Labels in user language, not internal jargon. Evidence for navigation design decisions that you can point to when someone insists the menu should be organized by department.