A GeoTree is a variant of a k-d tree, and stores data points that have a latitude and longitude, a unique integer identifier, and an optional 'weight' (e.g., the size of a city). GeoTrees are disk-based data structures and can store a very large number of points efficiently. If desired, for smaller data sets, memory-only trees can be constructed instead. The gem includes MultiTree, a GeoTree variant that supports queries at multiple levels of detail. For example, when focusing on a small region it can return points that would be omitted when querying a much larger region.