The most basic design rules are shown in the diagram on the right. The first are single layer rules. A "width" rule specifies the minimum width of any shape in the design. A "spacing" rule specifies the minimum distance between two adjacent objects. These rules will exist for each layer of semiconductor manufacturing process, with the lowest layers having the smallest rules (typically 100 nm as of 2007) and the highest metal layers having larger rules (perhaps 400 nm as of 2007).