I have used gmaps functions to fetch a list of longitude and latitudes for a (very long) list of delivery points for one of my customers.

I am attempting to calculate the centre of gravity for the distribution (not to be confused with the centre of mass of a physical object, this is a logistics term). So I did a simple mean average of the long's and the lat's and ploted these average values into a Google maps via a Hyperlink command. this works well and seems to make a kind of sense. For example I can filter out Scottish destinations and the CofG moves southwards as you'd expect.

I read online somewhere that given the earth is not flat and here in the UK we are quite a ways above the equator, the error could be relatively large.

If I assume the earth is spherical then I should perform some kind of cosine calculation to make it more accurate...

but of course the earth is not spherical either...

So my question is, How inaccurate is the simple mean average calculation I have done?

I am trying to find a suitable transport hub on a motorway near the CofG so a couple of miles out shouldn't be a massive problem. But if I have a potential error of many 10's of miles that would be more of a problem.

Any advice, thoughts or feedback is welcome.

Regards

Rob