Maptitude for Redistricting uses hierarchies to describe the relationship between nested layers for reporting.
You can use any area (polygon) layer as a selection layer in your plan. Simply choose the layer from the Selection drop-down in the Redistricting Toolbox. **Note: If the area layer was added after the plan was opened, close the Redistricting Toolbox using the x in the toolbox, and reopen it by choosing Redisricting>Redistricting Toolbox"