Boundary calculation

1. Is plan 1 and acceptable alignment of the 2 pages XLVI.3 & XLVI.7 that make up the 1921 Ordnance Survey plan?

2. Is plan 1 suitable to be used as a precise aid in any boundary calculation?

3. Is the alignment in Plan 2 any more accurate than the alignment on Plan 1?

4. Is the line shown between points A & F on Plan 4 an accurate translation of the corresponding lines shown on the 1921 Ordnance Survey plan?

Thank you for your letters dated 22^nd and 24^th March 2010, requesting comment on the mapping provided. We are pleased to provide the following information in relation to you request:

Firstly, some general points: We would draw your attention to the fact that Ordnance Survey mapping does not depict legal property boundaries nor do we attempt to show property ownership on our mapping.  As indicated in our previous correspondence, it is the Deed Plan which is the definitive indication of the alignment of a property boundary. 

The Ordnance Survey map is a topographic map only, but is used by Land Registry in identifying the property to be registered and in providing an indication of the physical features to which the legal property boundary may be related.

The features shown on Ordnance Survey maps represent the physical hedges, fences, walls, buildings, etc. present on the ground at the time of survey.  These are depicted within the limits of accuracy and portrayal possible at the scale of survey; (1:2,500 in the case of the mapping examples for this case).

Land Registry advises that any dispute concerning property boundaries or the extent of registered land should be brought to their attention at the earliest stage, to establish if they can assist in resolving the matter.  Ordnance Survey does undertake survey work on behalf of Land Registry, if Land Registry feels that this is required in assisting with the identification of land to be registered.  This relates only to the mapped position of physical features however.

In relation to your specific questions, we answer these in our opinion having viewed the mapping you have supplied to us:

1.   We accept that plan 1 is a fair alignment of the two pages in the immediate vicinity of the properties in question.

2.   We do not believe that plan 1 is appropriate for the precise definition of a property boundary at the level of detail implied in this case, based upon the information provided.

3.   We do not consider that the alignment in Plan 2 is any more accurate than the alignment on plan 1.

4.   Though, by inspection of the 1921 plan, it appears that the feature shown between points approximating to A and F on Plan 4 was a hedge, and which may be fundamentally the same hedge which appears today, we are unable to comment as to whether the line shown between points A & F on Plan 4 is an accurate translation of the corresponding lines shown on the 1921 Ordnance Survey plan,  The following may further explain our views in relation to this:

When examining the maps in question it is necessary to bear in mind:

a)  The scale of survey of both the 1921 and the 1975 (and later) editions is 1:2500, for which the smallest plottable distance using the manual surveying techniques of those times, is approx. 0.4m. 

b)  Changes in direction of alignment a ground feature amounting to less than circa 0.5m are effectively undistinguishable at the scale of the map over short distances.

c)  In surveying the alignment of a hedge, Ordnance Survey seeks to survey the centre of the alignment of the roots, as far as this can be distinguished, and subject to the limitations of the scale of the map.  Given that this centre alignment can have small irregular deviations along its length it is a convention to depict the alignment to reflect the generality of the centreline position where the variations are within the tolerances of survey at the map scale.

Nevertheless careful alignment of the adjacent County Series map sheets, and taking account of distortions introduced through various iterations of copying and recopying the paper map editions, suggests that the hedge was most likely to have been initially surveyed as effectively a straight line between the positions approximately corresponding to points B and E on the ABA site plan.

In the intervening period to 1975 and subsequently, the normal growth and regeneration of roots of the hedge, coupled with trimming at various stages and to varying degrees of severity, together with any normal maintenance of the hedge by replanting or natural seeding, may well have resulted in some slight variations to the physical alignment of the hedge on the ground.  However these variations are very likely to fall inside the tolerances of survey at the scale of 1:2500.

During the 1975 and subsequent revisions, the Ordnance Surveyor will only have made a revision to the depiction shown on previous maps if there were clear evidence to merit a revision of this feature – such as a new or visibly modified structure or alignment.  Small, semi-natural changes would not, of themselves, highlighted to the surveyor the need to make a substantive revision to the alignment of the hedge feature already depicted.

It follows therefore that during the 1975 (and subsequent) revisions, the alignment of this hedge feature has continued to be depicted as a straight line between the points corresponding approx B and E on the ABA plan.  We therefore believe that there is consistency of depiction between the various editions of the Ordnance Survey large scales plan of this area.

It is not possible to state with any certainty that the depiction of the area on a plan at a scale of 1:100 in December 2009 is an accurate representation of the features depicted on a plan surveyed at a scale of 1:2500 in 1921 or on any subsequent revision of mapping at this scale, because:

i)  Fundamentally different specification of surveying accuracy, precision and feature depiction will have been used in the two cases;

ii)  There is a considerable period of elapsed time between the 1921 survey and the 1:100 plan, during which time changes to the alignment of the feature(s) in question may well have occurred on the ground.

In general terms, it is not recommend reliance on a map at a scale of 1:2500 to determine fine detailed aspects of the alignment of a property boundary.  This is particularly the case when the alignments being questioned (as highlighted on page 4 of 7 of the ABA report), such as the relationship of point D to the linear alignment of points B and E in that illustration, are very close to the physical plotting tolerances in the original survey.

Please note that your enquiry has been processed to Freedom of Information guidelines. 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: FOI1058/March 2010