OS 25 inch 'blue-and-black' drawings, Scotland, 1890s-1940s
Further information

OS 25 inch 'blue-and-black' drawings, Scotland, 1890s-1940s graphic

We are very grateful to Dr Robert Wheeler for compiling this information below

Introduction - what are the 'blue-and-black' drawings?

From 1900, the OS usually drew new editions in black ink on a printing of the previous edition in light blue. When this was photographed, the blue would not reproduce. Thus lines from the old edition that were still needed were gone over in black, new ones added, and anything not wanted was simply left in blue. This preserved positional accuracy better than a tracing would have done, and it required fewer man-hours.

Actually it was a little more complicated, and it is these complications that render the drawings interesting. First, the drawing was not only in black. From 1901 a cadmium-orange ink was used for streams, so that (on the manuscript) they could be distinguished from fences. A cobalt-blue ink was used for certain things like parcel numbers on the foreshore, perhaps so that they could be reproduced or not according to the exact choice of photographic process. Also, we find a blue-grey wash used for building fill during the period when the printed maps showed this by stipple. Whether some automatic process was used or envisaged for converting the colour wash to stipple is an open question.

The second complication concerns those features like fortifications which the Ordnance Survey was directed not to show on its published maps. These features were surveyed, they were drawn and they were printed, the copies being for limited distribution. The features were then cleaned off the printing plate before sales copies were printed. It follows that these master drawings show them. To provide a warning that a sheet might require deletions to be made, drawings were stamped "This sheet includes War Office property" or similar. (see further information on security deletions below). In scanning the sheets at NLS, all sheets bearing such stamps have been scanned; additionally the whole of Nairnshire and Linlithgowshire have been scanned to show a representative sample of ordinary sheets.

The third complication is that, up to 1918, the blue impression was not normally from a sheet as printed but from associated manuscript material. This has the advantage that the blue as well as the black should be free from security deletions. Exactly what originals were used varies according to the date of the previous edition and whether it was a first or a subsequent edition.

From 1918 to 1921 the pre-1900 method of drawing called Card Revision was reverted to; additionally this might be used for sheets where there were very few changes. This method left no master drawing. Consequently there are printed sheets for which no drawing exists. The other way round, there are sheets which were drawn but never printed. However, one should not expect exciting revelations from them: most such drawings have no more information than appears on the derived six-inch sheet.

Two additional complications concern only small numbers of maps. There are three Fifeshire sheets of the 1890s included. Here the previous survey was intended to be drawn at the six-inch scale. To produce the new 25-inch map the draftsmen went back to the original surveyors' notebooks and replotted the data at the larger scale. A tracing of this would have been given to a reviser who would then have updated the map. Many aspects of the process are not fully understood and these drawings provide valuable evidence.

The other small group of maps are the Advance Editions. Because the measurement of areas was by parcels which might extend over multiple sheets, it was difficult to revise any one sheet without also revising the adjoining ones. After 1920, this was solved by giving the area on each sheet only to the edge of the sheet. An earlier approach to this policy involved publishing sheets drawn on this basis as an Advance Edition with the intention of updating them when the adjoining sheets had been revised and areas could be quoted in the normal way. These updates were made directly on the printing plate, the drawing being annotated in cadmium ink to show the changes required. Occasionally other changes like administrative boundaries might be made at the same time. These updated versions are generally not found in the NLS collection, so the master drawings may provide the only on-line record of them.

Security Deletions on the 25" County Series

The rules about what OS was permitted to show on maps sold to the public changed over the years and were conveyed in a number of Circulars sent out from Southampton. Not all these circulars survive, and there are in any case differences between the instructions and what actually happened. These notes are therefore based on what can be observed from the maps.

The Home Office, the Armed Services, infrastructure and industrial sites all need to be considered separately.

Home Office: Prisons

Unlike the Armed Services, the Home Office had no wish to see the internal buildings of their sites in the context of the surrounding terrain. Accordingly the interiors of HM prisons were not surveyed at all and remain a white space on all versions of the map.

War Department

The deletion of fortifications from published maps goes back to the early days of the County Series. It was implemented by means of a War Department Property note stamped in cobalt on the upper margin, which triggered a decision on what features might need to be deleted. Barracks did not usually require deletions; coastal batteries did.

A ban on showing height information within 5000 yds of a fort appears to have been introduced in the mid-1870s, with more site-specific rulings in 1881. This may explain the date of the note on the group of sheets around Fort George, where a radius of 3 miles from the Fort seems to have been applied. The deletion of heights caused controversy, even among the military; the rules were relaxed by the first decade of the 20th century, and dropped completely in 1928.


There was an Admiralty property stamp corresponding to the War Department one. Most Admiralty property concerned naval bases and armament depots, which the Admiralty certainly wanted deleted. These deletions could be carried out quite intelligently: for example, those features which were shown on the latest Admiralty chart could be shown in the same manner as on the chart. The Admiralty Chart of Rosyth (revised to 1919) serves as a good example.

By 1927, domestic sites around such bases were subject to the removal of names implying any association with the navy. Thus Admiralty Road at Rosyth is deleted and 'YMCA Naval Institute' loses the 'Naval'. This may have been a new policy: in 1915 it had been thought acceptable to retain Naval Base Junction where the branch line diverged.

Royal Air Force

Following the end of the 'War to end all wars' in 1918, most security deletions ceased. They were re-introduced from 1924, by which time the RAF had embraced the doctrine that any future war would be determined by a devastating bomber offensive. It is therefore unsurprising that it was insistent on the deletion of its airfields from the published maps. Perhaps uniquely, it sought to have fictional information shown rather than a tell-tale white space. Thus at RAF Donibristle the 'rough pasture' symbol is inserted.

Treatment of RAF property outside airfield perimeters can be quite intelligent. RAF Donibristle had its own railway running from a siding off the main line down to a jetty: this loses its RAF annotation but otherwise remains. The spurs to the airfield have been deleted but rather carelessly: the bar across the tracks at the points has been left.


From 1915 to 1918, gasometers were deleted, along with any names implying a gas works (eg. Denny Gas Works. Names were also deleted from electricity works. By 1926 the deletion of names associated with gas and electricity installations had been reintroduced. An unexpected benefit of being able to see these on the drawings is that we see the gradual crystallising of terms: 'electricity station' becomes the norm, whereas the equally logical 'gas station' dies out after a very few instances. Perhaps the clash with American usage had some influence.

From about 1935, the practice of labelling local transformers as 'Electricity Substation' seems to have come in. Since this name was one of those deemed to require deletion, it tends to dominate deletions from this date. One wonders who wanted these structures named in the first place.


A ban, introduced in 1915, on showing explosives works, extended to the deletion of names of associated chemical works. Tannoch Chemical Works (Dumbarton XXXIV.6) seems to be a case in point. The deletion of Engineering Works (Disused) on Fife XLIII.2 of 1927 may be an application of this policy, or it may be associated with the enthusiastic deletion of all names suggesting a naval linkage elsewhere on this sheet.

Oil storage was another matter of concern. By 1928, any group of circular oil tanks was liable to deletion as were all names associated with oil storage.

The other major cause of deletions was magazines at quarries and collieries: the building themselves were thought sufficiently anonymous but the names invariably vanished.