Although screen design is application dependent, appropriate graphic design principles and usability principles must be used in designing the actual screen layout. The menubar should contain strategic choices as menu elements that are consistent across different components of the system and across different interaction states. The workspace or canvas should contain overview diagrams and displays of information contained within a node. The feedback area should be used to keep the user informed about interactions, status of queries, updates etc. The control area should provide facilities to zoom, pan etc.