Surveying for 1976 County Series maps

Is the feature between xxxxxx and xxxxxx accurately mapped (on the LR screen print for Wxxxxxx) as the current feature on the ground which is a 6ft wooden fence? Please could you let me know how the OS maps for 1976 Country Series for xxxxxx was surveyed.

Thank you for your e-mail dated 25^th May 2010. We are pleased to provide you with the following information with regard to your request:

In relation to your question one, the feature between xxxxxx and xxxxxx, has been accurately mapped. This area of mapping was last updated by Ordnance Survey at some time during 2004. As you have advised me the fence between the above two properties was erected in 2002, the fence would have been captured as the ground feature at the time of survey, on the mapping to which you refer.

In relation to your second question, the two properties in question in xxxxxx,  lie in 1:2500 scale map xxxxxx.  This map was first published as a National Grid plan following post-war Overhaul in 1976.  Previously the area fell on County Series 1:2500 scale plan xxxxxx XLI/2 , the latest edition of which was the 1939 edition.

This County Series maps were surveyed on the Cassini Projection, using different reference meridians for different clusters of Counties.  When "overhauled" post World War II, these maps were recompiled onto a single Transverse Mercator Projection and the National Grid.  The recompilation for the xxxxxx area involved the "Cotswold Method" of semi-graphic adjustment, and a full revision by field surveyors utilising vertical air photographs enlarged to 1:2500 scale in addition to ground measurements. 

The Cotswold Method involved a precise co-ordinate comparison, in both projections, of the sheet corners of the County Series Maps, and of the mapped positions of the triangulation stations of the post 1936 re-triangulation of Great Britain.  Establishing the location of these key co-ordinated locations, and their surrounding map Country Series detail, in their correct positions with relation to the National Grid, enabled the remainder of the County Series mapping to then be graphically adjusted and compiled onto the National Grid, taking due account of the differences introduced between the two projections.

During the field revision process any identified local discrepancies between the mapped positions of adjacent features were rectified.

Please note that your enquiry has been processed to Freedom of Information guidelines.  As all requested information has been provided, we have determined that in all the circumstances of this case the Public interest consideration (section 17 FOIA) is not applicable in this instance.

If you are unhappy with our response, you may raise an appeal to our Appeals Officer at:

Complaints Team

Customer Service Centre

Ordnance Survey

Romsey Road

SOUTHAMPTON

SO16 4GU  

Please include the reference number below. The Appeals Officer will ensure that the process has been followed correctly, questioning any decisions taken regarding the original response and recommending disclosure of additional information if appropriate.

Thank you for your enquiry.

Reference number: FOI1072/May 2010