Previous research suggested that the apparent hierarchical organization of landmarks in an environment will influence subjects' judgments about spatial characteristics of that environment. We extended this previous work to a natural environment that has no predetermined, well-defined hierarchical structure. Using an algorithm that generates a hierarchy oflandmarks from recall protocols, we constructed hypothesized clusterings oflandmarks for a set of subjects familiar with the space. Then we tested these hypothesized clusters in a series of tasks, all of which required judgments about distances in the space. The results of these tests suggest that subjects do cluster landmarks on the basis of nonspatial attributes, and that the clusters have consequences for performance in various tasks that require access to spatial information.Create an image of the neighborhood in which you live. When you do this, some buildings and streets are included, whereas others are ignored. The selection of which landmarks to include in the image of a neighborhood is surely based on at least two criteria. One is the spatial proximity of the landmarks. Landmarks that are close together are likely to be represented together. But we speculate that your choice is based on more than just spatial proximity. We suspect that non-Euclidean information also influenced your selection oflandmarks. A typical person's introspective image of Ann Arbor, Michigan, for instance, may have the farmer's market, the train station, and the Broadway bridge form a subjective group. To be sure, these three landmarks are not far from each other physically. But Euclidean proximity is not the only variable that may underlie subjective organization: The Bell Tower and State Street in Ann Arbor are as close to each other as the other three landmarks, but they are not subjectively part of the same neighborhood. These introspections lead us to hypothesize that cognitive maps represent not only spatial information, but also information about some nonspatial characteristics, such as subjective clusters of landmarks.Of course, we need not rely solely on introspections to support this conclusion. There is evidence that impli-