The geography of airports can be broken into two key areas: the study of airport sites and the study of airport functions. The geography of an airport site looks at the airport at three different scales: international/regional/national scale, local scale, and site specific scale. At the international/regional/national scale the airport's location and function within a larger air transportation network is examined. Among the questions that may be asked include: is the airport a hub or spoke in an airline's network? What sort of market does the airport serve? The level of accessibility of an airport within the metropolitan area it services is at the core of geographic analysis of airports at the local level. The various components of the airport such as terminal design, gate placement, and services are the focus of site specific enquires, the third scale.
Physical geographic considerations are important in understanding the sites selected for airport construction. Large tracts of flat, obstruction free parcels of land are necessary for the construction of airports. A large amount of land is needed for such uses as aircraft operations (3000m runway for 747 to takeoff), terminals (some terminals are in excess of 2 km in length), parking (aircraft and automobiles), associated land uses (fuel farms, maintenance hangers, cargo storage, fire stations, etc.), and buffers to separate uncomplimentary land use (limit noise and other pollutants). Climatic variables such as wind direction and temperature extremes are other important geographic considerations. Finding large enough tracts of land to support airports is proving to be more and more difficult as urban areas grow. In addition to operation considerations airport developers and operators are cautious of other land use types surrounding the airport. As large tracts of land suitable for airport sites become scarcer, particularly in close proximity to urban populations, airports are being located farther out in the periphery of urban areas leading to issues involving accessibility. In some extreme cases, lack of suitable land leads developers to take such dramatic steps as creating man made islands in open water locations near Osaka, Japan and Hong Kong, China for airport creation. Airports are important components of not only the air transport network but also in urban systems serving as growth poles, drawing commercial, industrial as well as residential developments. In those cities where new airports have been built the old sites open up new devel opment opportunities. Airports Council International estimates that airports are economic engines accounting for more than $500 billion of economic activity in the United States in 2001, including 1.9 million direct and 4.8 million indirect jobs.
The function airports possess in air transport networks is an area of study of great importance to geographers. The various roles include hub airport, spoke airport, secondary airport, and niche airport. Depending on the dimensions of the network being studied airports may have multiple functions. The hub and spoke system and the role a particular airport plays in the network is one of the most important topics studied by air transport geographers.
There are two primary definitions of hubs currently used by geographers. The first defines a hub as a geographical area (airport) classified by the percentage of total passengers that enplane there (airport enplanements/total country's enplanements). The second definition is that a hub is a subjective corporate decision to concentrate resources with the object of interconnecting passengers to maximize profits. The goal of a hub and spoke system from this second viewpoint is to bring a large number of passengers from outlying points, assemble them at the hub and then fly them on to their final destination. In this definition, hubs are used to enhance the overall efficiency of a carrier's service and increase the number of serviced destinations. From a mathematical standpoint the use of a hub and spoke system by an airline allows the carrier to increase the number of destinations served from a hub airport geometrically instead of arithmetically.
Hub and spoke systems have both advantages and disadvantages when compared to a point to point system. Among the advantages is the ability of the hubbing carrier to offer a large number of destinations from hub airport, frequent service, large numbers of passengers flowing through the airport, and higher load factors. Disadvantages of this type of operational system include highly variable work demands, hub premium on fares, missed connections or delays impeding the entire network, high congestion at hub airports, and longer travel time.
The increase of importance of low cost carriers around the world in the last 20 years has led to the emergence of a class of airports termed 'secondary airports'. These secondary airports are usually within the same metropolitan region as larger, better known airports or were previously the primary airport for a region until a newer airport was built. Global examples of secondary airports include Chicago Midway, Dallas Love, Glasgow Prestwick, London Stansted, and Frankfurt Hahn. These airports are successful because their operations are focused on being uncongested and low cost, creating a distinct geographical network not generally duplicated by full service airlines.