Newsky uses proprietary passenger simulation system where each passenger is accounted for and realistic trends in route demand are reflected. Operations carried by airlines inside this system can affect these trends and change them completely. This is can lead to some routes being more or less popular than in real world but that's on purpose allowing airline managers to discover this and use to their advantage.
You can view current airport traffic situation and trends by clicking on the airport ICAO on live map.
Below is an example of traffic trend graph. Blue is the normal passenger distribution for given airport while green is the current situation. In this example we can clearly see that routes to the south are currently not in high demand and therefore will receive less than normal passenger count.
Fill factors act on top of trends and further affect how many passengers will buy a ticket for given flight.
There are currently 3 fill factors: