Compute distances based on LatLong data

Anonymous 

I'm no expert but...let me try

A not very geographically accurate calculation could be using the right angle triangle length formula of A^2 + B^2 = C^2

so the straight line distance, a.k.a radius, (since the earth is flat, as we all know all too well...) would be the square root of (Lat2 -Lat1)^2 + (Long2-Long1)^2 where the difference in coordinates is calculated in whatever distance metric (metres, KM...), using an appropriate conversion factor for both lat and long distances  based on the general geographical whereabouts (if you really need to fine tune the "radius", and can be easily found using two points in the sea with the same lat for lat and the same long for long), especially for the latitude, since the variation is relevant (equator vs. artic circle for example). 

At least, I think that is something which rings a belI from those 'oh so happy days at school way back when' last century.

someone please correct me if necessary!

PS: I don't think the earth's curvature will make that much of a difference over short distances, and it is an approximation after all