I'd meant to reply to Peter's paper a few days ago but been too
busy...
I thought Peter's paper was very useful and interesting. In
particular the points about metadata - we not only need a
content/terminology standard for spatial feature types, but must
also have one to record the source of the data, i.e. the way it was
captured and processed.
However there were a couple points that need raised, as they may
reflect wider perceptions (as maybe reflected in the subsequent
posting about SAM digitizing).
1. "... hand-held GPS kits which apply a spurious level of accuracy
to their results". Not true - a better way of putting it would be
"...which give results with a level of precision that is open to
misinterpretation". The accuracy of the various GPS systems,
hand-held or back-pack, with or without selective availability, and
with or without real-time or post-survey differential processing
are well documented.
2. "Data created against the background of a vector map...is more accurate than
that created against a raster map". In one very specific current circumstance,
where by 'raster map' Peter means the Ordnance Survey 1:10,000 raster data
available before the current release of LandPlan, and by 'vector data' he means
the OS LandLine data (at 1:1250, 1:2500 & 1:10,000), this will be true most of
the time. However it seems to be presented as a statement of general GIS theory
or principle, and as such is misleading. You could equally contrast the OS
vector Strategi data with the 1:50,000 raster mapping and say that raster data
is more accurate. It totally depends what the data is depicting, how it was
created, and what it is to be used for.
If anything a wiser caveat is that vector data, because it can be displayed
convincingly at any scale, is more subject to misuse and misinterpretation at
inappropriate scales than raster data, which, as Peter notes, has limited
viewing range due to monitor limitations.
The implication of this for the conference discussion is that spatial metadata
should always include information about the mapping from/against which any
dataset/feature is captured (though this is standard GIS good practice already,
not specific or new to archaeology).
Regards
Crispin
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