Check the box next to ‘Top Elevation’ to use a constant value as the aquifer top elevation for the cells over which the zone extends, or import scatter point data (shapefile or txt) for spatial interpolation across the zone feature. Click the '...' option button for more details regarding scatter point import / interpolation. (Note: the scatter point interpolation tool is ideal for DEM data in point shapefile format.)
Similarily, check the radio box next to ‘Bot Elevation’ to use a constant value as the aquifer bottom elevation over which the zone extends, or import scatter point data for spatial interpolation.