As accurately as possible is the important point, surely in most cases 10m is close enough. I dislike "accurate" boundaries which make it easy for the planners developers. There is no site marked in field A so we can develop there. Why we can't admit that we do not always know where the sites are?

In the case of SAMs the scheduled area often does not cover the whole area of archaeological interest.

>>> [log in to unmask] 12/10/2001 09:26:17 >>>
I would have thought that it is important to locate monuments etc as
accurately as possible.  Certainly for planning applications you need the
most accurate representation when deciding whether or not to ask for
archaeological work.  There is little point in asking for work in an area
which lies within an archaeological site merely because of an error in
representation, or vice versa in not asking for work in an area of
archaeological interest just because it lies immediately outside an
innacurate boundary.  For SAMs the small scale of the maps on which the
boundaries are marked is of course a problem here and I have exactly this
problem at the moment in attempting to decide whether or not an application
for an extension lies within or immediately outside a SAM.

 Similarly for previous excavation trenches there are cases where one would
wish to relocate previous excavation trenches in order to excavate an
adjacent area etc so the most accurate representation possible is needed.
As an aside, however, I have generally found that old excavations/trenches
etc are innacurately plotted, due I suspect to the original surveying using
temporary survey points - third tree in the hedgerow, field gate etc -
rather than taking a large scale map out into the field and plotting the
trenches directly on to this, but this is a completely different bee in my
bonnet!

----- Original Message -----
From: "garibaldino" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, October 10, 2001 10:41 PM
Subject: Re: Where we are. Understanding data and positional accuracy issues
a t RCAHMS - Part 2 and Summary


> Ok as its gone quiet I'll ask a quick question.
>
> When digitising SAM's should we be digitising them based on Raster data or
> digital data? As E Lee pointed out, it is only neccessary to put on both
> maps to see the disrepancies between the two. And whilst we have argued
> about the SAM polygons versus the full description being the monument, I
am
> using this example, I think, to highlight a wider point.
>
> Given that something is mapped/planned on a more inaccurate base map(ie
> raster data), should we correct that in the office to match to more
accurate
> digital data, or should we be using the same standard for polygonising (ie
> stick to the Raster data) until/unless we can re-survey to a more accurate
> standard whatever the polygon is supposed to represent? As an example, if
a
> polygon of an event covers a field on the raster map, can it be mapped
using
> the digital boundaries of that field and still be correct? Is that even a
> valid question or have I missed the point here?
>
> My gut reaction would be to stick to the more inaccurate standard until
the
> original data can be re-surveyed (if that is possible, which in the case
of
> eg Excavation trenches it may not be), to represent the fuzziness of the
> data. Any other views?
>
> Nick Boldrini



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