Re: Surveying in the UK

The UK is small enough to be covered by one datum, the Ordnance Survey (OS) Grid
Reference System.  It's featured on all of the "Landranger" series of maps
published by the Ordnance Survey at a scale of 1:50,000.  (National) Grid
References take the form of  SP 123321, or more accurately SP 12344321, where
the two letters indicate in which large (100km) square the following Eastings /
Northings pairs of figures give the position to 100m or 10m respectively.  The
false origin is to the SW of the UK, and the grid north is set to align with
true north roughly through the middle of the country - and it's not through the
Greenwich meridian.
Most, if not all other, maps published by the OS also include the grid.  Hand
portable GPS units from Garmin and others include the grid.  There are base
stations providing GPS differential type of reference info.  Heights are
available for measured points (bench marks and triangulation points) and on
earlier maps this info was published on the map.  Nowadays, I think you have to
purchase the information from the OS, if you want it to a high accuracy.
Triangulation points (slim concrete truncated pyramids sited on high ground) are
being allowed to fall into decay as GPS is used.
Bench marks are typically chiselled into side walls of bridges, walls etc.
Occasionally I've seen metal plates bolted into vertical surfaces, and domes set
into areas adjacent to dams.  Height above MSL is to the horizontal feature of
the chiselled mark, which has sloping legs, as in the ASCII art following:
___
/    \

Land in the UK was not parcelled out by so many square yards etc. as it was in
the US, so surveying here takes on a different form to what happens in the US.

-- 
M Stewart
Milton Keynes, UK
www.megalith.freeserve.co.uk/oddimage.htm


"Paul" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> I was hoping some one may be able to assist me. I am moving to the UK
> in approximately one month and hope to obtain work as a land surveyor.
> But in the mean time can anyone tell me if there is a national or
> regional coordinate system in place in the UK. I am guessing it would
> be possibly managed by ordnance survey. How does one get access to the
> values of this network and how the positions are ground marked?