|Quoting Bennett123 (Reply 8):|
In other words O & D is simply a return journey with no intermediate stops
No, O&D for a city/airport refers to the passenger traffic either originating from that city/airport or whose final destination is that city/airport. For a city-pair or airport-pair it refers to passenger traffic that originates at one of the cities/airports whose final destination is the other city/airport. Round trips would be origin traffic for both cities/airports as well as destination traffic for both cities/airports, whereas a one way journey would be origin traffic for the starting city/airport and destination traffic for the other city/airpot. Intermediate stops along the way are not part of origin or destination traffic for the stopover city/airport as long as the passenger continues on his way without leaving the airport. Passengers transfering to a connecting flight at a city's airport or transiting through on the same plane are not part of O&D traffic for a city/airport.
O&D traffic for a given city is important because it indicates how much non-connecting traffic a particular city can generate, either from residents from the city and surrounding region departing from and returning to the city or from visitors coming to the city/area and going back to their city of residence or another city. It is a measure of the captive audience that a city/regional market can provide. O&D traffic between a city-pair is a measure of how much traffic travels between two cities regardless of whether the trip has stops or is nonstop. It is used to determine what aggregate capacity on the route between those cities, either non-stop or through a hub(s), can be supported, and whether nonstop flights are warranted or not.