Transition Altitude and Transition Layer
In New Zealand the transition altitude is 13,000 feet. If you are flying at 13,000 feet or below you need to set your altimeter to local QNH. If you are climbing above 13,000 feet then passing this altitude you must set your altimeter to 1013 Hpa.
In New Zealand we have a transition layer, this extends from 13,000 feet up to FL150. Aircraft climbing through 13,000 feet set their altimeter to 1013 Hpa. Aircraft descending below FL150 set their altimeter to the local QNH. Because it is possible for aircraft flying through the transition layer to be using different altimeter settings, level flight within the transition layer is not permitted i.e you can not file FL140.
A diagram is shown below