Airlines are notoriously difficult businesses to run.
Each and every flight operated is a multi-thousand dollar gamble on whether or not passengers will buy tickets.
Aside from cost, the strongest factor for customers on which flight they will take is often the overall travel time, so airlines put enormous effort into properly assembling their puzzle of flights so they can offer the shortest connection time possible.
With so many destinations all across the world, it's just natural that most routes require connections so airlines need to attract connecting passengers in order to stay in business.
Now, most flight connections for traditional airlines happen out of their hub airports.
American Airlines, for example, has 10 across the United States and every single one of their flights either begins or ends at these airports.
But not all hubs are created equal.
Charlotte Douglas, Reagan National, and LaGuardia are largely built for north-south traffic and terminating traffic, Miami is for connecting North American travelers to flights to the Caribbean and South America, Philadelphia is a bit of a hybrid hub connecting both north-south traffic and North American traffic onto flights to Europe, JFK is the major hub for connecting North American traffic to European flights, and the Los Angeles hub's main purpose is to connect North American traffic to Asia and Oceania bound flights.
But then there are these three—Chicago O'Hare, Dallas-Fort Worth, and Phoenix Sky Harbor airports.
These three airports are the truly important connection airports since they lie between the coasts and their schedules reflect this.
