1. A computer-implemented method, comprising: identifying, from an index structure stored in memory, a reference minimum bounding shape that encloses two or more minimum bounding shapes, each of the two or more minimum bounding shapes corresponding to a data object associated with a corresponding leaf node of the index structure; and accessing the index structure using the reference minimum bounding shape, the accessing including representing at least one minimum bounding shape of the two or more minimum bounding shapes in a relative representation calculated relative to the reference minimum bounding shape.