[OSM-dev] Question about Calculating Radius from GPS cord

[Fire Girl]

I am working with OSM data, and would like to be able to spec out 5 mile
bounding boxes from certain GPS points.

After research into this problem, I am to understand that each degree of
latitude is approximately 69 miles (111 kilometers) apart with a slight
variance (68.703 - 69.407 miles) between the equator and the poles, and
that each degree of longitude is widest at the equator @ 69.172 miles
(111.321 kilometers) and gradually shrinks to zero at the poles. : ) :)

So what does this mean?  If I want to take a input point, like lets say,

167.9 lat
-29.1 lon

or

-63.1
18.1

Can someone say with authority, what the 'calculus' would be to
definitivly construct a NSWE bounding box with a 5 mile radius around
those points?.... that would be basically close enough or accurate? :)

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