In practice, to all intents and purposes in most terrain other than wide
open plains etc the radius of the earth is so large in comparison to the
distance one can see that the "arc"on the surface (even assuming the earth's
surface was smooth) is seen to all intents and purposes as a straight line.
Anyway, if one is surveying one is measuring in straight lines anyway
("Lines of sight") almost by definition. (That is unless we get really
esoteric and wonder about atmospheric refraction or whether the earth's
gravitational field has a measurable effect on light, but let's stay
In effect, if one draws a sufficiently large number of sufficiently short
lines at rightangles to a series of large radii the resultant polyhedron
will eventually approximate to a circle for all practical purposes.
If on a spherical body the sectional view would be an arc, but the plan view
would still be a straight line, cf "great circle" routes for aircraft.
Sorry, I'm an engineer who has been recycled as an archaeologist! You
probably had this sussed all along and just had your tongue in your cheek.
----- Original Message -----
From: "Bea Hopkinson" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, March 31, 2001 2:29 AM
Subject: Re: Roman Roads, a query
> Now wait a minute, to be even pendantic, we are talking Roman here and
> they still held the peripetatic and flat earth view, so they wouldn't
> be thinking in arc's. But i guess what you are saying Mark is that
> whether they liked it or not their straight line became arc'd. Somehow
> can't envisage how that would work out in practice?
> On 3/30/01 2:41 AM John Wood writes:
> >>>> Mark Bell <[log in to unmask]> 03/30 9:41 am >>>
> >To be absolutely pedantic the shortest distance between two points on the
> >Earth's surface is an arc (a section of a circle).
> >Any "straight" line drawn on a map is actually a curve. This is one of
> >best arguments against the existence of lay lines!
> Beatrice Hopkinson 73071,327@compuserve