O  r  d  n  a  n  c  e    S  u  r  v  e  y






We have all grown used to maps and the road atlas to find our way around the country and of course these are all based on the Ordnance Survey maps which cover the whole country.
As most people realise the Ordnance Survey actually make these maps by dividing the whole country up by way of a grid. However, what is not so generally well known is that the start of this mapping process or triangulation, as it is called, was started just outside Salisbury.










Old Sarum Earthworks
On the A345 road to Marlborough, just outside Salisbury, 300 / 400 metres north of the entrance to Old Sarum earth works, you will find this stone commemorating the feat.
That initial line measured by Captain Mudge in 1794, and known as the Salisbury Plain base line, was 6.93 miles long, and with a similar line in Ireland ( Lough Foyle baseline 7.89 miles ) the basis for present day mapping was formed.
This was all I knew about the stone, and despite having visited the site to take the original photo, I was unaware of the following part of the story due to crops growing in the field at the time of my visit.






The following two photographs are by Mr Foster Telford of nearby Wilton, who told me that Captain Mudge had a cannon cemented upright into the field, so the top became both a solid, and permanent base, on which to mount his surveying equipment. This end of the 'line' is still shown on any 1:50,000 map as 'Gun, End of Base', and the top of the gun is still visible and in place to this day, behind the memorial stone. Captain Mudge incidentally later went on to become Director General of the Ordnance Survey.






The inscription reads:-

"In 1794
a line from this site
to Beacon Hill was measured by
Capt. W Mudge of the Ordnance Survey
as a base for the triangulation of
Great Britain "


Photo by Foster Telford of Wilton,
Nr Salisbury.

Co-Ords: 414220 132940 / SU 142329  

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