Dear Scottish Colleagues,
Forgive me for asking, but what is the archaeological theoretical reason for mapping things (presumably "sites") to sub metre accuracy ?
Firstly, there is the hoary old debate of should we be identifying "sites" with boundaries rather than continuous distributions of finds and/or processes across the landscape ? What is the point of accuracies of cms when people of the past inhabited landscapes without absolute measurements ? Who cares whether a Scottish long house is located at X or Y cms west of the Greenwich meridian. Does cm accuracy give us any better understanding of why the long house was built at that location or its relationship with other long houses in the vicinity ?
Then there is the issue of context. Even the OS says its maps are only good to an accuracy of 2-4 metres, so if you map a site to greater accuracy, it won't fit properly on your GIS, unless you do the OS's job of mapping everything else to the same accuracy. Do you have a digital terrain model (DTM) to fit your height data to ? And even the DTM won't be accurate to sub metre standards. Why is it that EH states that its SAM maplets are only indicative and it's the textural description that is the legal boundary. Because the real, contextualised description is actually more accurate, more meaningful and interpretable than any virtual reality map. For most of the past, things were positioned relatively, not geodetically. The geodesic or geodetic locations of things from the past are entirely idiomatic and unamenable to archaeological theorizing, in contrast to their positions in mental and natural landscapes. We have a long way to go yet before moving from processualist archaeology to post-processual cognitive archaeology, it seems.
Not least there is the question of resources. Just exactly how many "sites" do you have, with clearly recognised boundaries that aren't yet mapped accurately (a bit of contradiction there but necessary to justify use of GPS) that would justify the expense of £6K (or even £24K)? What is the cost per site ? Or if you are mapping archaeological features, what added value or return from your SMR will be created by mapping at sub-metre accuracy compared with the 2 metre accuracy of plotting from OS maps? I accept that spot locations for rock art and cairns on open moorland are best plotted by GPS, but I would certainly want to see a cost-benefit analysis for spending big money on GPS.
That's my contribution to blue skies debate for today.
cheers,
Neil
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