Newburg is more of a business- and financial-class city than the city of Fairfield is. It is filled with shops, apartments, and businesses in the downtown districts. Several tall buildings and skyscrapers can be seen in the downtown skyline and because of all the business and size of the city, Newburg has its own airport allowing the businesses to thrive and expand globally as well as easier access for the public to enter and leave the city as they wish.
Due to the fact that buildings are still up in massive flames and the heavy presence of ember in the air, along with Bill commenting on the military bombing that occured in the city, Newburg was only recently besieged by the Infection.
Due to the high risk of infection, numerous planes are seen crashed throughout the city by the Survivors due to the Infected or from military bombings.
Alternatively, Newburg is part of the Pittsburgh area, since it takes place near a river (at the Boathouse Finale, you can see Newburg across the river), has an international airport, and Pittsburgh is, in real life, close to Allegheny National Forest, which is the location of the next campaign, Blood Harvest.
There are actually 5 Newburgs in Pennsylvania, however all of them don't fit the description of this Newburg. Most likely, this Newburg is based of Pittsburgh.