The NETDRAW procedure expects all the network information to be contained in the Network input data set named by the DATA= option. The network information is contained in the ACTIVITY and SUCCESSOR variables. In addition, the procedure uses default variable names in the Network data set for specific purposes. For example, the _X_ and _Y_ variables, if they are present in the Network data set, represent the coordinates of the nodes, the _SEQ_ variable indexes the turning points of each arc of the network, and so on.

In addition to the network precedence information, the Network data set may also contain other variables that can be used to change the default layout of the network. For example, the nodes of the network can be aligned in the horizontal direction using the ALIGN= specification, or they can be divided into horizontal bands (or zones) using a ZONE variable.

Table 9.15 lists all of the variables associated with the Network data set and their interpretations by the NETDRAW procedure. Note that all the variables are identified to the procedure in the ACTNET statement. Some of the variables use default names that are recognized by the procedure to denote specific information, as explained previously. The table indicates if the variable is default or needs to be identified in the ACTNET statement.