Make sure each Area_datum has a unique symbol (for the sake of the colorblind).
Check available housing in City:;:get_chance_to_birth().
Remove defunct open_buildings[] and closed_buildings[] from City.  Init tax_rate[] to 0, except 50 for CIT_PEASANT.
Remove defunct labor_pool from City.
Change the misleading "contains" to "may contain" in Interface::display_area_stats(AREA_MINE).
In Interface::building_status(), check whether the area the building belongs to is closed.  If so, include this in the name and display the maintenance as "---".  If maintenance is zero, display the maintenance as "0.0".