With deadlines to meet and huge distances to cover, traveling by road is not an option. At such times, air travel is the option that most people go for. It saves a lot of time, which is the most important commodity today. Many airlines have air miles reward programs, as an incentive to frequent fliers.
There was a recent movie titled 'Up in the Air', starring George Clooney, which showed the obsession that these programs create among frequent fliers. Many people, like the guy played by Clooney, literally live out of suitcases. They spend half of their lives in travel. For such people, the reward programs are really useful. You get points, every time you travel, which you can cash in later and travel for free. It helps if you can calculate air miles and have a log or record. If not for the reward program, you an at least keep it as a reminder of the time you have spent flying from place to place, around the world.
Air Vs. Land Miles
There is one big difference in calculating air and land miles. The difference obviously arises out of the fact that planes fly and cars are driven on roads. Planes need not wind around obstructions like lakes and mountains. Roads keep winding around, which makes distance calculation difficult. That is why, calculating air miles is simpler than calculating road miles and both have different ways and units of measurement. Google maps can calculate road miles for you online.
The unit used to compute air miles is the 'International Nautical Mile'. One international nautical mile is a distance of 1852 meters. The origin of this unit is in the fact that one such mile is the distance spanned across one arc minute of latitude, along a meridian. This is different from the geographical mile, that is normally used as a unit of length.
One international nautical mile is approximately equal to 1.151 geographical miles. As Earth is not a perfect sphere but an oblate spheroid, the distance of a latitude arc minute, across a meridian, is not constant, but changes with latitude. That is why, the 'average' distance is defined as the 'International Nautical Mile'.
There are many ways of calculating air miles. One way, is to actually gather all the data related to your journey and calculate the distance on your own. This will involve getting information about the flight path and exact coordinates of the airports, which will be your departure and arrival points. Using a scaled map like the Mercator's map and using the Rhumb line (great circle) method, you can compute international nautical miles.
The second simpler technique is to use services offered by Internet sites like 'Webflyer', which can give you an answer, at the click of a mouse. All you need to do is enter information about your initial and final destinations and it will compute the miles between those two cities.