When trellising a map chart, it would be good to have each trellis panel to zoom into the relevant area rather than all of them showing the complete map.
e.g. If trellis by country you don't want to see the complete world map in each trellis panel but in the panel for the U.K you'd want to the the U.K. only and in the panel for the U.S. the U.S. only and so on.
e.g. If trellis by "region" on a wafer you don't want to see the complete wafer in each trellis panel but you want each panel to zoom-in each region.