Survey of kerb lines

Dear Requester

Request for information – FOI12289

Thank you for your letter dated 20^th May 2012.  Ordnance Survey does hold some of the information, and in answering your questions, it is most convenient to deal with them in the following sequence:

1.         Enclosed Map Extract - accuracy

The map extract you have provided is of the 1:500 Scale Ordnance Survey Town Plan of Brighton of 1876-77.   These maps were produced for a number of major town and city centres across Britain during in a short period of the 1860s – 1880s.  The driver for mapping at this “civil engineering” scale was to provide high quality information to assist the major works of public sanitation and development planning in an era when Victorian engineering was seeking to bring order to the rather chaotic urban developments of the industrial revolution era. However the costs of these surveys were borne by individual town authorities and few town maps were revised, the mapping gradually falling into disrepair save where the urban development has remained largely untouched for 130 years or so, as appears to be the case in your area of Brighton.

The maps were surveyed using chain survey methods.  This meant that a network of triangulation stations were established across the town or city from which straight line measurements could be taken either directly to another such point.  Considerable ingenuity was required to provide a sufficiently close network of triangulation points for the survey, but only rarely was it necessary to survey by means of a series of “dog-legs” known as traverses, along very crooked alleys and streets. Here the angle of the change of direction of each dog-leg was measured using a theodolite and the traverse plotted out rather as the course of a sailing ship ‘tacking into the wind’ can be plotted. 

Each straight chain line was measured with a surveyor’s chain measuring 66 feet (22 yards) in length and comprising 100 links of 7.92 inches.  Along the length of the chain line intermediate measurements recorded the position of right angled offsets which were measurements to the ground features (house corners, fence junctions, kerb lines etc.) which needed to be included on the map. The aim of the chain survey was to establish a skeleton framework of map detail which, when plotted onto a master trace for the area in question would enable a field surveyor to complete the map using alignments of previously surveyed and as yet un-surveyed detail, together with reference measurements and direct plotting of these by hand onto the master trace to build up the map detail.

Then overall aim was to ensure that the positions of the adjacent features on the finished map were within the tolerance of the smallest plotable distance at the scale.  Typically this is of the order on 0.2mm which represents 0.1m (approx 4 inches) on the ground. 

However it is important to remember that the resulting master copy was then transferred to a printing plate and the printed “Chart paper” editions printed.  Chart paper is susceptible to stretching and shrinkage due to changes in atmospheric conditions and the map you have copied will of course have been stored in one or more locations for the past 135 years before you took your copy, so it will not produce scaled distances to the tolerances of the original survey.   

2.         Survey of kerb lines

We do not hold formal records of the detailed specification used by Victorian surveyors, but can apply modern specifications with some degree of confidence.  

Typically today, a clearly defined kerb line of kerbing stones indicating a distinct change in height compared to the adjacent roadway, will be surveyed by a pecked (broken) line if less than 0.3m in height.  More substantial kerbs, clear steps from road to pavement and safety fencing along kerb-lines are shown by solid lines.  Similar concepts may be applied to Victorian surveys with reasonable confidence in a majority of cases. 

However, it is important to bear in mind the scale of mapping and the concept of minimum separation distances in considering the specific example you have identified.  In order to ensure clarity of information at the 1:1250 scale, to which the post war large scales mapping of Brighton has been undertaken by Ordnance Survey, we have applied a minimum separation of 1.0m between adjacent features.  Hence if the kerb line lies within 1m of the end wall of the adjacent house, then Ordnance Survey will omit the kerb line since the depiction of the two lines side by side would lead to a lack of clarity of the mapping information.

3.         Relationship with Land Registry information

Ordnance Survey maps do not depict land and property ownership boundaries and the depiction of roads, tracks and paths on Ordnance Survey maps is no indication of a right of way, since the mapping makes no statement as to ownership or rights of access over land.  Hence while our map specification may result in the depiction of only a selection of features from the landscape for reasons of cartographic clarity, the equivalent land registration documents, which take full cognisance of the deeds of the property when registered, may well depict ownership extending to alignments not included by Ordnance Survey.

Finally inspection of aerial and terrestrial imagery available to me, showing this access route, suggests that while the portion of land you describe is indeed coloured differently, (in pink) than the adjacent ‘roadway’, there is no clear difference in height between the ‘road’ and ‘pavement’ that would merit surveying as a kerb line, even if we disregard the minimum separation distance issue.

Your enquiry has been processed according to the Freedom of Information Act (FOIA) 2000. As all the requested information has been provided or is not held by Ordnance Survey, 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:

FOI Appeals Officer
Customer Service Centre
Ordnance Survey
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Southampton
SO16 0AS

E-mail: foi@ordnancesurvey.co.uk

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The Appeals Officer will inform you of the outcome of the internal review within 40 working days, in line with the Information Commissioner’s guidance. The Appeals Officer will either: uphold the original decision, provide additional explanation of the exemption/exception applied or release further information, if it is considered appropriate to do so.

Appealing to the Information Commissioner’s Officer (ICO)
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