This paper concerns methods for indexing areas in twodimensional array data. A method for naming subpictures from rasterscan image data is presented with notation that eases their subsequent storage access. Equations are given for converting each subpicture name into a storage-location pointer. A function ``NUMERIC'' is described that aids this task. Algorithms enabling efficient retrieval of subpicture areas from sequential and direct access files are presented. Examples are given that show that improved retrieval response is possible from using NUMERIC to sort lists of areas to be recalled. The paper includes an overview of tree data structures, the subject implemented by these techniques. An overlapping picture subareas storage scheme is discussed.