> When John parked out the front of my house, I was *amazed* that
> the arrow pointed to the exact position within a foot or so.

JT> The spec is +/-15 metres RMS 95%. That means it'll be within a
JT> 15 metre radius, 95% of the time.

JT> Typically, it's within about 5 or so.

 When it first became available, kit was 100m, and the military
version that called in another satellite to get 1m, but I think they
all do that now...

> On the small scale, the Earth is as good as flat. Mapmakers
> really do understand that the planet is round... they use flat
> maps but fudge the drawing so it works.

JT> I'd say it's more likely so you don't need to do any heavy duty
JT> mathamatics while on the road. On a UTM grid, you can pretty
JT> much lay out a flat ruler and determine the distancy between
JT> any two points with accuracy, anywhere on that map. 

 Yair... they fudge positions to make it fit, flat.

JT> Of course, you get some severe distortions if it covers a large
JT> area, but for smaller maps, it's ideal.

 Yair. If you look at Africa on a Mercator flat projection, and
Siberia, Africa is *much* larger on a globe, and stretched out so the
bottom half ismuch bigger, and Siberia (and Canada) is *much* smaller.

 Anywhere you're likely to drive in a car, is as good as flat.

Regards,
Bob

--- BQWK Alpha 0.5