A computer aided design system can determine coverage of a metal layer mosaic. The system can apply a tile pattern to a design including at least one layer. Then, the system can identify at least one tile of the tile pattern that violates at least one first design rule. After that, the system can apply a sub-tile pattern to an area identified in the identifying the at least one tile of the tile pattern that violates the design rule. The system further can identify at least one sub-tile of the sub-tile pattern that violates at least one second design rule. Finally, the system can apply a deep-sub-tile pattern to an area identified in the identifying the at least one sub-tile of the sub-tile pattern that violates the second design rule.