There are a number of pre-defined environmental conditions called scenarios for each watershed. Associated with each scenario is the TPM used to predict land cover change. These scenario files are located in the directory indicated by the LUCAS_DIR environment variable. As is done for the list of available watersheds, the LUCAS GUI parses the name of each file in the LUCAS_DIR directory to build a list of scenario names. The scenario names are then displayed to the user in a Motif XmScrolledList widget. The user chooses a scenario other than the default by pointing-and-clicking on the scenario name. When the user chooses a scenario, a description of the scenario is displayed in a Scenario Description interface. It is important to show the description of the scenario to the user since the description is normally too long to capture in the scenario title.
Each of the XmScrolledList widgets used in the LUCAS interface has its XmNscrollBarDisplayPolicy resource set to XmAS_NEEDED, which indicates that scrollbars will be displayed only if the workspace exceeds the clip area in one or both dimensions. This allows the interface to place multiple text strings into a small interface window.