How to Calculate the Distance Between Two Points on Earth
The great circle distance or the orthodromic distance is the shortest distance between two points on a sphere (or the surface of Earth). In order to use this method, you need to have the co-ordinates of point A and point B. (The great circle method is chosen over other methods because it provides a greater accuracy.)
First, convert the latitude and longitude values from decimal degrees to radians. For this divide the values of longitude and latitude of both the points by 180/pi. The value of pi is 22/7. The value of 180/pi is approximately 57.29577951. If you want to calculate the distance between two places in miles, use the value 3,963, which is the radius of Earth. If you want to calculate the distance between two places in kilometers, use the value 6,378.8, which is the radius of Earth.
Find the value of the latitude in radians:
Value of Latitude in Radians, lat = Latitude / (180/pi) OR
Value of Latitude in Radians, lat = Latitude / 57.29577951
Find the value of longitude in radians:
Value of Longitude in Radians, long = Longitude / (180/pi) OR
Value of Longitude in Radians, long = Longitude / 57.29577951
Get the co-ordinates of point A in terms of latitude and longitude. Use the above conversion method to convert the values of latitude and longitude in radians. I will call it as lat1 and long1. Do the same for the co-ordinates of Point B and get lat2 and long2.
Now, to get the distance between point A and point B use the following formula:
Distance, d = 3963.0 * arccos[(sin(lat1) * sin(lat2)) + cos(lat1) * cos(lat2) * cos(long2 - long1)]
The obtained distance, d, is in miles. If you want your value to to be in units of kilometers, multiple d by 1.609344.
d in kilometers = 1.609344 * d in miles
Thus you can have the shortest distance between two places on Earth using the great circle distance approach.