28th June 2012, 04:01 PM
RedEarth Wrote:how many times have I found myself attempting to relate something to a drawing I presumed accurate that was produced by an architect or similar? Even the OS mapping is sometimes remarkably dubious when compared to something actually surveyed. A superbly accurate trench plan, for example, isn't much use if the OS map it is going to be related to isn't very.
As for the point of the survey, I'm not sure, probably just something else to make us feel inadequate!
Humm I think your comments sort of make the point it is worth understanding that architects are not surveyors they draw what they think should be there. As for trying to fit a trench surveyed at 1 to 10 on an OS map surveyed at 1: 2500 I am not surprised you are having problems. If you want an accurate frame work go back to the OS control frame work which is accurate to mm or use GPS. OS digital map data is again only accurate to the scale at which it was surveyed it is no good blowing up 1:1250 mapping to another scale such as 1:50 and expecting it to have the same tolerances as mapping surveyed and plotted at 1:50. Understanding the origins of your base map or your control stations is crucial to accurate surveys.