It seems there is an error on the zoning maps when it comes to district centre. Throughout the relevant documentation, the district centres in the city are listed as Mahon, Douglas, Wilton, Blackpool and Ballyvolane. In the zone maps, all are marked as "ZO 08 District Centres", except for Douglas which has been mistakingly marked as "ZO 07 Urban Town Centre" (as seen on Maps 6 and 7)