Some embodiments of the invention provide novel methods for representing items in a design layout. For instance, they use a method that identifies several half-planes, that when intersected, define the shape of the item. Some embodiments use a method that (1) identifies a first set of location data for the item with respect to a first coordinate system, (2) identifies a second set of location data for the item with respect to a second coordinate system, and (3) specifies the item in terms of the first and second set of location data. In some embodiments, both the first and second coordinate systems have first and second coordinate axes. Some embodiments use a method that receives a first set of data that defines the item with respect to a first coordinate system of the design layout.