A two dimensional (2D) matrix symbology for use with bar code and other optical readers. A finder structure includes a center square and a plurality of nested squares having centers that approximately coincide with the center square. A symbol descriptor located adjacent to the finder structure encodes data indicating the size of the symbol and the length of the message encoded therein. A reference grid extends throughout the symbol to facilitate the location of individual data elements with respect to the finder structure thereof. The data structure of the symbol is filled with data blocks which are organized into layers which surround the finder structure. Data encoded in the data blocks may be read sequentially within layers and between layers. The symbology is a versatile symbology in that the number of check data blocks is user selectable to provide the desired level of error correction.