City Codes will be unique. There is an ISO coding system for most major City level geographical locations but there there stills needs to be the ability to create our own if no ISO code exists. The system should auto generate a code if the user does not define one. If the code is changed at a later stage, the system should automatically reflect the change as everything should be tied to the ID. So if the system generated a code 123 and this was later changed to NEG then everything that was 123 would change to NEG automatically.

Where no Region Code is used when defined an accommodation, the system will refer to the City Table. So for Montego Bay in Jamaica, there will be an Airport Code of MBJ and a City Code that is also MBJ. When accommodation is defined and the systems picks up that there is more than one location with the code being defined, the user should be prompted to confirm what type of location. Most often this will be Airport or City. If a user then wanted a hotel or holiday to Madrid in Spain, as both the City and Airport have the code MAD, they would be asked if they wanted a City accommodation or Airport accommodation.

You can see here that there is a possible combination of Region type such as Florida which is a state in the US and the Canary Islands which are made up of 4 main Islands but actually come under Spain so they would be defined in the Region table rather than the Continent table.