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Can anyone impart wisdom and correct me if my interpretation is incorrect.
I have a topographical survey detailing existing and proposed heights for land. What do the figures actually mean. I am pressuring each figure is height above sea level and that a figure like this, 10.40, suggests the land is 10 metres 40 centimetres above sea level.
Thoughts?
That is correct if the datum is taken from [url= https://en.wikipedia.org/wiki/Ordnance_datum ]AOD (Above Ordnance Datum) which is MSL (Mean Sea Level)[/url], it could well be an arbitrary datum set b the surveyor that's effectively a local grid.
Not necessarily..
There should be a datum point marked on your drawing and all elevations will be relative to that..
If it is relative to sea level they will likely be marked AOD.
[url= https://en.m.wikipedia.org/wiki/Ordnance_datum ]https://en.m.wikipedia.org/wiki/Ordnance_datum[/url]
Generally I'd expect it as m above sea level (it should be to OS coordinates (usually)) AOD
It should say in the legend may also go on about scale factor , nowt to do with scale of the plan, more to do with the OS fudge factor to cram the UK into the errrm UK.
You are right, 10.40 wold be 10m and 40cm (10.4m)
Thank you - I suspect it is AOD as we are around that elevation. Doesn't appear to be anything on the plan to confirm so I will query it with the surveyor. Thanks for the links at least I now know what questions to ask.
Is that the distortion of scale due to making a flat map of a curved planet, or something else? In my understanding, OS maintain the scale, and you correct for direction (variation).scale factor , nowt to do with scale of the plan, more to do with the OS fudge factor to cram the UK into the errrm UK