Move-In Hearse
Ghost Population is different from the normal 
Citizen Population. It can only be increased by building Halloween Residences. To allow more Ghost population in your city, you need to build Halloween Community Buildings.
When expanding, your Ghost Population will be combined with your normal Population.
Once the Halloween (2012) event ends, the ghost population/allowance will be added to your total population/allowance and ghost citizens will change to regular citizens.