Geometrical layout data structures.
A layout is a hierarchical structure. Its purpose is to efficiently represent the geometrical properties of a silicon chip. Hence a layout consists of ‘cells’ which hold geometrical shapes such as polygons on multiple layers. Cells also hold instances of other cells (recursion is not allowed though). Typically a cells correspond to standard-cells or macros and will be instantiated possibly many times. Each cell instance also holds the placement information, i.e. the location, rotation, mirroring and possibly magnification.