1. Floating Topic
2. the Great Circle
   1. Meridian
   2. equator
3. Other than the Great Circles
   1. parallel latitude
4. Distance Between 2 points
   1. on the Great Circle
      1. difference in angle x 60
   2. on the parallel latitude
      1. differece in angle x 60 cos latitude
5. Speed
   1. Unit : Knot = nautical mile per hour