Phil Newman describes the unpredictable accuracy of hand held gps and 
suggests that it cannot be compared to an accurately measured survey. Wrong. 
The accuracy is not unpredictable. In upland areas with a clear view of the 
sky an accuracy of 5-6m is normal. When that accuracy is examined for 
example by recording the same point on several different days and comparing 
the results it can be demonstrated that although the position does change it 
is by a very small amount and when averaged 5m accuracy often equates to 
+/-2.5m or better.

When I first started using GPS some 5 years ago I was very sceptical about 
how accurate the results were and what the accuracy quoted by the instrument 
really meant. By experiment and by comparing my surveys with others I am 
confident that it is a valid and reliable method of survey. It is therefore 
an accurately measured survey within the limitations of the accuracy of the 
instrument just as any other accurately measured survey is. As I am aiming 
to plot at a scale of 1:2500 a position error of 5m in the real world is 2mm 
on the plan. Just like transcribing air photos this technique produces a 
plot that shows a feature in approximately the right place, approximately 
the right size, and approximately the right shape. It is not the same as a 
1:500 hachured earthwork survey but it is not trying to be. See Lead Mining 
Archaeology in the Yorkshire Dales, Landscapes vol 4 no1 Spring 2003, and 
The Greenhow Hill Lead Mines Survey, British Mining 73, 2003 for examples of 
the application of GPS to landscapes survey and A Survey of the Area Around 
Jamie Mine, Sunside Allotment, Appletreewick, British Mining 71, 2002 to see 
that I do also use detailed earthwork surveys.

Just to stir things up a bit in 1995 Paul Everson, who was at that time a 
surveyor for RCHME and therefore may now be one of Phil’s colleagues at 
English Heritage, wrote that over detailed field survey rather than 
providing more answers, can “produce unhelpfully undigested heaps of 
information”.

Mike suggested that producing plans in GIS is difficult. Not so as he well 
knows and has seen. Importing the GPS data as points and simply joining the 
dots is not difficult and talking about pencil drafts of plans is just 
being, pedantic. No doubt the miserable old git will have further comments 
to make so can I suggest that now that he has had a go at the archaeologist 
he might want to find another victim so that I can get on with some work.

Martin Roe

President, Northen Mine Research Society,nmrs.co.uk

Conservation Officer NAMHO, National Association of Mining History 
Organisations, http://www.namho.org

Lead Mining in the Yorkshire Dales, 
http://www.martinroe.pwp.blueyonder.co.uk

Meerstone Archaeological Consultancy 
http://www.martinroe.pwp.blueyonder.co.uk/meerstone.htm