2)Manaco
GT uses standard geometry to calculate distances (as you would expect. More info -> http://en.wikipedia.org/wiki/Pythagorean_theorem) Here are two tips related to this simple math formula:
1) When you move on an angle it take 1.4 moves. (the square root of 1^2+1^2). This is good. If you could not go on an angle it would take 2 moves. But it is more than one move. This means that 1 angle move "takes up" 2 non-angle moves. What is the tip? Well, two angle moves take 2.8 moves -- so if you move once at an angle it is "free" to move the second time at an angle.
Because of the math, you should always move on angles in multiples of 2 to get the maximum movement from your units.
2) 176 is the square root of 250 squared divided by two. Why does this matter? 250 is the range of a jet. Thus a unit located at 0,0 can hit 176,176 with a jet (that sector is 250 away.) If a sector is less than 176 in the X and the Y of your air base you can be sure your jets will reach it. (Note that if x or y is more than 176 it might be that a jet can hit it if the other co-ordinate is low enough)
To find out if a given location is within range do the following:
Find the distance for both the x and the y.
Find the square of both of these numbers.
Add those two numbers together.
Take the square root.
If this number is less than 250 you can hit that location with your jets.