A comprehensive computer-aided mask layout technique has been developed which permits quick conversion of LSI circuits into working photomasks. It is an efficient solution to the problem when the demand for customized circuit layouts greatly overshadows the more standardized techniques. No computer background or programming experience is required. This approach allows the designer to quickly compose high-density mask layouts using simple free-hand line symbols. These easily drawn symbols, representing complex circuitry, utilize a standard device-level building block library which simplifies the conversion of LSI circuits into photomasks, and permits the designer to generate up to 100% of the layout without leaving his desk.