1. A method for use in characterizing areas of interest in overhead imagery, comprising: decomposing, using a processor, a plurality of pixels of at least one input overhead image into a plurality of components of a first hierarchical data structure, wherein the input image is associated with a geographic area; deriving, using the processor, at least one image descriptor for each of the components; and constructing, using the processor with at least some of the image descriptors, a second hierarchical data structure that includes a plurality of hierarchically-arranged levels of nodes, wherein the nodes of the second hierarchical data structure are arranged into a plurality of leaf paths that each extend from a root node to one of a plurality of leaf nodes, wherein each of the image descriptors depends from one of the plurality of leaf nodes, wherein each node at a particular one of the levels is a respective visual word, and wherein all of the visual words at the particular one of the levels collectively comprise a visual dictionary.