Computing distance using lat/long coordinates
The distance returned is the arc length of a great circle connecting the two points, essentially air miles. Note that latitude and longitude are in degrees. Latitude is in degrees north of the equator; southern latitudes are negative degrees north. Longitude is in degrees east of the prime meridian; degrees west are negative degrees east.
To see how spherical distance is calculated, see these notes. To see how much difference it makes if you take into account that our world is not exactly a sphere, see this post on ellipsoidal distance.
You can look up your latitude and longitude here.
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