# Connectivity

Use the connectivity page to specify the conductor layers and their connections. On a conductor layer, all touching or overlapping shapes are connected. A connection is made between conductor layer when the shapes of the two conductor layers overlap. Optionally a via layer can be specified which must be present to make a connection between the two conductor layer.

To specify a conductor layer

- Use "layer/datatype" notation to specify explicit GDS layers and datatypes.
- Enter the layer name to specify either a named layer or a symbolic layer. Symbolic layers must be defined in the symbol table (see ) and can be computed from boolean expressions.
- Instead of using a symbolic layer, enter a expression directly without defining a symbol (see ). Inside the expressions
  - Use "layer/datatype" notation to specify an original layer with explicit GDS layers and datatypes.
  - Use the name to specify a named original layer or to refer to a different symbolic layer defined in a symbol entry.
  - Use the operators '+', '*', '-' and '^' to specify logical OR, AND, NOT and XOR respectively. The precedence of evaluation is '^' and '*' before '+' and '-'.
  - Use round brackets to group expressions.

By creating conductor layers with boolean expressions, it is possible for example to separate an active area layer of a CMOS transistor into source and drain regions by subtracting the gate poly. Symbolic layers are useful to use "speaking" names for layers instead of the numeric layer/datatype specificiation. Please note, that the net tracer is considerably slower when using boolean expressions.