From: John Tserkezis 
Reply-To: Fidonet AVtech Echo 

Bob Lawrence wrote:

> Br> The real problem with the UBD, is that like all street
> Br> directories, they are drawn for readability, and not accuracy.
> Br> As you know proper topographical maps allow for the curvature
> Br> of the earth ( I forget the technical [ mapping ] term for this
> Br> ), whereas the UBD and other directories are drawn so they can
> Br> write the street name in the space provided :) Still it can be
> Br> usefull. 
> 
>  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.

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

  Typically, it's within about 5 or so.

>  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.

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

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

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