Friday, 21 March 2014

Landmark’s data team solve latest OS mapping mystery

Celia Craven, a key part of Landmark’s data team, recently solved a mystery surrounding an unrecognised symbol on an OS map, alerted to us by one of our clients.  The symbol (※) seemed to have no objective reference in historic map legends and subsequent googling only lead to more misinformation. 

It seemed like there would be no resolution…until Celia got her hands on the mapping.

The mapping in the area is derived, as Mr Peter Hobby from Ordnance Survey informed Landmark, from multiple map sheets. Using this information, combined with the indication that these are hand-drawn annotations, Celia was able to analyse the area logically to and determined the potential nature of the symbol. The addition of line features to distinguish map sheets from one another was also useful in this instance, both as a visual aid and a significant clue.

If we consider the nature of surveying and the methods applied to this process (historically at least) we can hazard an informed guess that the symbols are indicators of field area values where only partial elements of the field were available to the surveyor.

An example of this is depicted below – the coloured partial field object contains the mystery symbol. The line cutting through the map indicates the boundary of a map-sheet.

The red polygon and the symbol (with associated value) conform to the measure of the field only as it’s depicted on the southernmost map-sheet.  Perhaps the surveyor at the time was not able to measure the full extent of the field and was only able to capture the extent of the field as it appeared on their map? We can’t say for certain - that’s just speculation on our behalf.

The northernmost map-sheet and its acreage value (2.971) is for the entire field. The shaded area value (1.198) is for only the field area available on the map-sheet.  Applying this logic to the other areas divided by the map-sheet line is also true.

The original query map corroborates this finding as it’s divided by four map-sheet divisions.  Here we can see a total field measure (3.914 acres) and the partial values in each map-sheet.

The south-western map sheet (from 1918) shows .388 and .128.

The south-eastern map sheet (from 1919) shows a total of 4.112 and a partial value of 2.728.

The north-western and north-eastern maps sheets were surveyed at the same time  (1923) so depict the same value of 3.914.

We can’t say for certain, but it seems the symbol represents a marker for a partial field measure.

Whilst some of us were excited at the prospect of X marking the spot Celia provided the balance of intelligence and logic that resolved the mystery. Whilst there is no buried treasure (seemingly) this minor revelation does indicate something previously hidden to us in the present, the ingenuity and diligence of mapping surveyors and the real-world work carried out by Ordnance Survey and their team of experts. These symbols were marked on maps by an individual, or group of individuals and the results of their work are still visible to this day.
 
 

 
 
 
At Landmark, we live and breathe data 24/7 – it’s our DNA after all. If you have any mysteries you need help solving, please contact one of the data team via askdata@landmarkinfo.co.uk.


Daniel Lewis-Carter
Data Information Co-Ordinator
Landmark Information Group

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