Catalogue description Ordnance Survey: Directorate of Field Survey: National Grid Object Name Books

The Object Name Books are arranged by reference to their related map sheet numbering, the style of which depends on the map scale:

(a) References to the largest scale mapping at both 1:1250 and 1:2500 scales can be found in one set of books since they both relate to the 1 km squares of the National Grid. The 1:1250 series paper map sheets are numbered as quadrants of the 1 km grid square which in its entirety is covered by a single 1:2500 series map sheet. The style for the 1 x 1km sheet numbering is e.g. SE5439. Between 1960 and 1990 they were published in 2 x 1km form with the sheet numbering quoting both sheet numbers, eg. SE5439 + SE5539 which was expressed on the sheet as SE54-5539.

(b) Each sheet of the 1:10,560 and 1:10,000 scale mapping for mountains and moorland areas covers an area of 5 x 5km and is labelled as a quadrant of the 10 x 10 km National Grid square, e.g. SH65SW.

(c) The sheets of the small scale mapping at 1:50,000 are numbered 1-204 inclusive and relate to the Landranger Series numbering. These sheet lines were established to cover the country in the most economical way, and some are close matches to the old Seventh Series 1:63,360 (one-inch) sheet lines. Hence in 1972 some Seventh Series ONBs were renumbered and the content extended to suit the 1:50,000 Series; others were dismantled and appropriate sheets included in a new 1:50,000 Series book.

The economies imposed on Ordnance Survey (OS) after the First World War unfortunately coincided with new legislation on land registration (1925), town planning (1925), land drainage (1926), slum clearance (1930) and land valuation (1931) all of which required accurate mapping for implementation. By the early 1930s it became clear that OS had been left ill equipped to supply sufficiently accurate and up-to-date maps. A Departmental Committee under the chairmanship of Sir J C (later Lord) Davidson was therefore set up in 1935 to consider how to restore the effectiveness of the national survey.

The final report of the Davidson Committee was published in 1938. Its major recommendations included:

• the introduction of a metric National Grid as a reference system for all large- and small-scale maps;
• the introduction of a metric National Grid as a reference system for all large- and small-scale maps;
• the recasting of the 1:2500 (25.344 inches to one mile) scale map series on national instead of county lines using a national projection rather than the separate county projections which had caused problems of fit and accuracy along county borders;
• the introduction of a system of continuous revision for large-scale maps;
• the testing of a larger 1:1250 (50.688inches to one mile) scale of survey for densely populated urban areas;
• the trial of a 1:25,000 (2.5344 inches to one mile) medium-scale map which, if successful was to be extended to cover the whole country;
• retention of the 1:63,360 (one-inch) mapping but recast onto the national projection and incorporating the National Grid reference system.

The implementation of these recommendations, which were to form the basis of the OS's operations for the next 40 years, was however to be delayed as the Department again took on its military alter ego on the declaration of war in September 1939. Ordnance Survey's HQ took several direct hits during heavy air raids in Southampton on the nights of the 30 November and 1 December 1940. A vast quantity of irreplaceable material was lost; the buildings were severely damaged, and many were completely destroyed.

The end of the war saw Ordnance Survey's attention turned back to civil mapping requirements. High on the agenda were the Davidson Committee recommendations. Priority was given to the new 1:1250 scale mapping and the first sheet was produced in 1947; within a year 100 sheets at this scale had been published. The face of the map carried the OS National Grid, which was subsequently a feature on all OS maps. OS maps were now constructed on a national projection, the Transverse Mercator Projection, and were indexed to the network of squares which formed the National Grid. This Grid provided the first truly national map referencing system by which any place in the country could be given a unique location reference number.

The first National Grid 1:10,560 (6-inch) scale maps were published in 1946. These, like the National Grid 1:2500 scale maps first published two years later, were recompiled from old County Series sheets. The scale of 1:25,000 had been used on military maps as far back as 1913 and now appeared on the OS National Grid in 1945 in an experimental map of the Poole area. The map was a success and coverage was extended to the majority of the country. This became the Pathfinder and Outdoor Leisure Map Series.

Putting Davidson's ideas into practice required a massive reorganisation within the OS, both in the office and in the field - especially since the revision of the framework of vertical and horizontal control points on which the national surveys are based (the Retriangulation of Great Britain begun in 1936) was ongoing until 1962. Aerial photography, first tried experimentally for the revision of some 1:2500 mapping in 1925-26, was now a major new factor in land survey.

A more systematic approach to keeping abreast of changes on the ground was introduced to replace the traditional cyclical revision. A network of small survey offices, known as Continuous Revision sections, was set up across the country. These provided surveyors with a more secure base compared with the nomadic life of resurvey work, enabling them to maintain a constant vigil on ground changes in the locality and to survey and record those changes almost as they happened. These offices were controlled from regional headquarters located at London, Edinburgh, Harrogate, Nottingham, Kidderminster and Bristol.

In 1964 OS decided to embark on a full metrication programme for all National Grid large-scale mapping. By 1969 ministerial approval had been obtained for metrication of the height and area data on new and revised maps at 1:1250 and 1:2500 scales, and the first maps were published in the 1:10,000 Series replacing the 1:10,560 (6-inch). Metrication of the small scale 1:63,360 (one-inch) followed with the production of the First Series 1:50,000 maps (largely based on a photographic enlargement of the existing Seventh Series 1:63,360 mapping on new sheet lines), and the Second Series 1:50,000 maps which incorporated design and content changes in keeping with administrative area changes (Local Government Reorganisation Act, 1972), changing market needs and technological developments.

The programme of National Grid large-scale mapping began in the early 1940s and until 1962 was mostly concerned with the new mapping for urban areas. It was completed by the early 1980s by which time the first Ordnance Survey digital map at the 1:2500 scale had already been published.