A data structure suitable for interactive placement of disjoint rectangular objects is presented. Area available for placing new objects is described in terms of a unique set of maximum empty rectangles (MERs), each of these MERs bounded by objects already placed or by the boundary. Algorithms for addition and deletion of objects have been developed. Deletion is achieved by using the addition procedure itself. Information can readily be derived from the data structure to identify regions where a given object may be placed, to determine whether a new object can be placed if an existing one is removed, to assess restrictions on linear dimensions and areas of objects that can be placed etc. Though the scheme has been developed for automated layout of PCBs and ICs, it is applicable to other areas such as layout and modification of shopping centers and cities, utilization of warehouse space etc. A distinct feature of the method is that the extent of search to update the data structure need not increase with the number of objects placed or with the density of placement.

Ordering of connections is one of the key areas in automated layout design of printed circuit boards. A simple heuristic algorithm to decide the priority of connections is discussed in this paper. It makes use of six interference matrices to calculate a measure of the interference a connection causes to all other connections on the board and this forms the basis of the ordering.