Architectural drawings using CAD (Computer Aided Design) consist of lines, text, numbers, shapes and other geometrical objects. For the purposes of LEGION model building, only the lines and shapes that are true obstacles to pedestrian movement are strictly relevant.

For example, hatching marks or lettering in a CAD drawing will act as obstacles to LEGION Entities if they are imported into LEGION Model Builder and retained during a simulation. Removing these extraneous lines and marks (or moving them to a different layer designed to carry such details purely for presentation purposes) is called 'cleaning' a CAD plan and the resulting plan is said to have been 'pedestrianised'. CAD that retains the original architectural lines can be used for presentation purposes after a simulation has been successfully run. This type of CAD is known as 'Presentation CAD'. For more information on CAD plans, see Using CAD .

Any information in the CAD drawing about the walking surface that would normally be expressed with lines (for example staircases, escalators or ramps) must be communicated to Entities using Spatial Objects in place of the original CAD lines.