A city record in Master data is a location. This field is used on different screens to indicate a location where shipping or transport actions may take place. When creating a city record, ticking the ‘Is Port’ check box defines whether a city record is used to designate a port location. If "is Port" is ticked, the city will then be shown in a port list depending on if a port field is required for the Delivery term. Example:
Selecting ‘Preferred’ will make a city rank on top of any cities drop-down list.