Newburg is more of a business and financialclass 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 of the business and size of the city, Newburg had it's 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.
Once the Infection reached the city, CEDA immediately quarantined the main source of travel to the city in the hopes of preventing the spread of the Infection once again. This method failed and the military ordered an immediate bombing of the city to prevent further Infection. While the Survivors made their way through the city in order to follow a C-130 Hercules military plane to Metro International Airport and escape from the Infection, they crossed many rooftops, went through the abandoned hotels and office buildings and even through a construction site.
Due to the fact that the 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 occurred 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 towns named "Newburg" in Pennsylvania. However, none of them fit the description of this Newburg. Most likely, this Newburg is based on Pittsburgh.