History of the International Collection

Modern mapping from aerial photography was considered to be an important contribution to the development of British territories after the Second World War. The Air Photography, Map and Survey Record Archives of The Ordnance Survey International Collection were created over a period of 53 years, from 1946. In that year the Directorate of Colonial Surveys (DCS) was established by the Colonial Office as a central survey and mapping organisation for British colonies and protectorates. In 1957 DCS was renamed the Directorate of Overseas Surveys (DOS), to reflect the imminent decolonisation of many British territories. Some non-Commonwealth countries, most notably Ethiopia, Liberia, Sudan and Yemen Arab Republic, were mapped by DOS between 1975 and 1991. Government reviews of DOS’ purpose and activities during the 1970s led to the winding up of the organisation as an independent body in 1984 and its merging with Ordnance Survey^®,  under the title Overseas Surveys Directorate, OS (OSD).

By 1991 the last significant aid-funded mapping projects had been completed by OSD and all survey parties had been disbanded. OSD’s title was changed to OS International; its main activity became consultancy, mainly in Eastern Europe, while traditional map production gradually declined. OS International was wound up as an independent unit in 2001.

Aerial photographs, maps and survey data were kept in discrete libraries at DOS, Tolworth, but on relocation to Ordnance Survey in 1984 were amalgamated into one working collection called Technical Information and Support Services (renamed International Library in 1991). Following a review in 2002, Ordnance Survey decided that the International Library was no longer needed for operational purposes. Responsibility for supervision of the disposal of these public records then passed to TNA who, together with OS staff and with advice from specialist bodies, set about appraising the material and determining which of the records should be kept and where. Public access to the Library in Ordnance Survey head office ceased in March 2003.

During 2003 and 2004, Ordnance Survey and TNA sought suitable custodians of parts of the collection and relocated them. Public access was progressively re-established from the end of 2004, and is now fully restored.

Air photography archive

This archive is now held at the British and Empire & Commonwealth Museum in Bristol, and a duplicate set has been entrusted to Oxford University to further global climate change research.

About 1.5 million monochrome, vertical aerial photographs of survey standard, suitable for viewing stereoscopically in 3-D, are held in the Collection. Most photos are at nominal scale 1:30 000 – 1:60 000 and are in 230 mm by 230 mm format. Although mainly panchromatic, there are some infra red, together with some monochrome prints, off colour or infra-red negatives, and a few colour prints.

Nearly all the photography was taken for topographic or land use mapping purposes, but the sources and scales varied over the years. Some of the earliest cover held was flown by the United States Army Air Force and the US Navy over Caribbean and Pacific islands during the Second World War.

Almost all photography of Africa, Aden, Malaya and Borneo flown between 1946 and 1953 was taken with Fairchild^® K17 cameras of 152 mm focal length, and from 1951 with Williamson F49 cameras of the same focal length. These were carried in aircraft (mainly Lancasters) of RAF photographic reconnaissance squadrons. Throughout the period the planned scale of photography was 1:30 000; this was selected as a compromise both to provide specialist departments (for example, geology, forestry and agriculture) with photography that would permit the interpretation of thematic information, and to suit topographic mapping. Only a small number of sorties were flown to obtain photography at a scale larger than 1:30 000; for example, of the Volta River delta and dam site, 1:5000 scale in 1946. Gee-H radar was used in Africa and Aden to navigate the aircraft along a series of concentric flight lines around a ground radar station. Visual, straight-line navigation was used only occasionally in Africa,for example, for large-scale photography of the Freetown Peninsula, Sierra Leone, and in British Somaliland for some 1:30 000 scale cover.

Contract photography, flown by British commercial air survey firms using visual navigation methods, was first taken in 1949 and predominates from 1953 onwards. Over 200 contracts were let by DOS, each one usually covering the area of a proposed mapping or land use project but, especially in the Caribbean, sometimes extending over several countries and at several different scales. The scale of photography for 1:50 000 scale mapping after 1954 was usually 1:40 000, but from the 1960s, with increasing use of super-wide-angle (89 mm) lenses, photo scales were often smaller, 1:50 000 or 1:60 000. Large-scale mapping areas were photographed at larger scales, for example, 1:12 500 photography for 1:2500 scale mapping blocks. Photography was sometimes flown at scales larger than 1:40 000 for specialist interpretation purposes, for example, 1:25 000 for forestry interpretation.

In addition to contract photography, cover obtained by the national survey departments is occasionally held, together with that flown for other aid agencies such as the Canadian International Development Agency. Later RAF photography, sometimes at very small scales, is held, and also some Royal Navy photography. For many areas more than one set of cover, of various dates, is available for research into environmental change – for example, geomorphology, vegetation, communications and settlement – over a 40–50-year time span.

Most of the photography that was used by DOS for mapping, including all the older RAF cover and all contract cover, is indexed on a series of record reference cover diagrams, generally at 1:500 000 scale. The written catalogue is a Roneodex card index, with one card per film, recording camera and lens type and number, calibrated principal distance, film type, flying heights, dates of photography and so on.

A small-scale guide to the main areas of such photography is given by the maps at the back of the DOS Annual Reports from 1951 to 1984,  to be held by TNA. Other photography held in the collection, and some not held, is shown on non-DOS cover diagrams or sortie plots produced by the originator of the photography. Summary diagrams for each country illustrate the location of all photography. The principal points of photos used in the mapping are shown and numbered on almost all DOS 1:50 000–1:125 000 scale topographic maps and provide the most accurate indication of the location of individual photos. Air photo mosaics and print laydowns (uncontrolled mosaics produced as map substitutes on standard sheetlines in advance of the regular mapping) are held in the map archive at the British Empire &  Commonwealth Museum alongside a duplicate set of DOS mapping

Technical records held include camera calibration certificates, film reports with dates and times of photography, and contract documents. The film negatives of RAF and RN photography are held by the RAF; those of contract and other cover are held by the national mapping agency concerned, except in the case of British Antarctic Territory, for which the films are held by the  British Antarctic Survey, Cambridge,

A small amount of satellite imagery, mainly Landsat but some SPOT, is also held.

Map archive

The collection contains all series produced by the DCS and its successors (DOS, OSD, OS and OS International, abbreviated here as DOS) between 1946 and 1999. It includes superseded DOS editions and other agencies’ editions in series produced jointly by DOS, national mapping agencies and British Military Survey; also, series – mainly geological – printed by DOS for third parties. Although the great majority of the maps are topographic, there are significant holdings of geological and land use mapping. Other thematic map coverage includes climate, soils and population. All of these are now held by the Royal Geographic Society with the Institute of British Geographers (RGS-IBG).

The basic scale for most former British territories was 1:50 000, but smaller scales were used in arid lands such as British Somaliland (1:125 000) and parts of Botswana (1:125 000, later 1:100 000), and larger scales ( 1:25 000) in Mediterranean and Caribbean islands. selected="selected" areas, and sometimes whole islands (Malta, Gozo, Bermuda), were mapped at 1:2500 scale (occasionally 1:5000, 1:2400, 1:1200) and, rarely, at 1:500 scale (Male, Stanley). A small-scale guide to the main areas mapped by DOS is given by the maps at the back of the DOS Annual Reports from 1951 to 1984; the later maps (1967 onwards) indicate areas where there is both pre- and post-1960 mapping. Sheet indices exist for most series.

DOS topographic mapping is supplemented by a range of print laydowns (PLDs), which are uncontrolled mosaics of air photographs, usually at 1:125 000 scale. They were often produced as map substitutes, on standard sheet lines, in advance of the regular mapping, mainly using 1940’s–1960’s aerial photography. They provide a synoptic view of relief and vegetation patterns in more detail than the maps and more conveniently than using the original contact prints. This archival set of PLDs is unique in its completeness as it was not formally published or supplied to Copyright Libraries.

International boundary maps, and the associated DOS international boundary files, have been selected for permanent preservation at TNA, Kew .

The DOS map library catalogue and finding aids were originally a written catalogue in Kalamazoo^® binders providing access at series level, while all individual sheets (covering less than the whole country) are marked up in scale order on graphic composite indices to provide rapid access to the mapping that is available for any particular part of a country. The original Kalamazoo binders will be at TNA. The unique DOS series number books (two vols) and post‑1960 master graphic catalogue will also be held at TNA.

The DOS maps from the collection have been re-located to RGS-IBG, which now holds a complete set designated as The Ordnance Survey International Collection Map Archive.

Non-DOS mapping

Non-DOS series, mainly produced by national survey departments and held in the original OS International Library, do not form part of the OSIC map archive at the RGS-IBG.

Those series have been offered to academic institutions throughout the British Isles.

DOS progress folders

DOS progress folders are not in the map archive either, but are mentioned here because they relate to map production. Dating back to the early 1950s, the progress folders contain the technical notes and minutes relating to each project or block of mapping. Contents include full details of the plan control and aerial photography used, the technical correspondence and internal minutes on the progress and accuracy of the mapping, the techniques used in construction of the maps, the maps used as source material and so on.

The progress folders have been presented to the Charles Close Society Archive, located in the Cambridge University Map Library.

Survey record archive

DOS field parties worked at one time or another between 1946 and the late 1980s in almost all of those countries, establishing ground control (planimetric and height) for mapping, observing national primary and secondary survey frameworks, and assisting with tertiary and cadastral control and levelling. Incorporated in the collection are the results of control surveys by other organisations, some connected to DOS schemes and most used by DOS in its mapping programmes. Records of field work by the Falkland Islands Dependencies Survey and the British Antarctic Survey, formerly held by the DOS Survey Data Library, are now held by the  British Antarctic Survey, Cambridge. The other records mentioned below will be held at TNA.

The information contained in the survey data files is summarised in master trig diagrams (Mtds), master control diagrams (MCDs) and master control Cards (MCCs), which were designed to permit the rapid retrieval of coordinates and so on for all plan control known to DOS in any specified area.

30th Meridian triangulation in Africa

The records of the Arc of the 30th Meridian triangulation in Africa, filed under code AD rather than by individual country, are mainly those of the 1930’s observations by Major Hotine (later i/c Retriangulation of Great Britain, Director of Military Survey and Director of Colonial Surveys) and others in East Africa, but include work dating back to 1903 and up to DOS Tellurometer^® scale checks of 1963. The 30th Arc records include correspondence, observations, diagrams, computations and results.

The survey data archive

The survey data archive is organised by country and subject in the following classes (an asterisk indicates only sample files or abstracts are being permanently preserved at  TNA):

The DOS survey data catalogue

The DOS survey data catalogue occupies 49 Kalamazoo binders. The master control diagrams (MCDs), generally at 1:500 000 scale, show the position and classification of every astronomical, trigonometrical or Doppler station for which coordinates suitable for 1:50 000 scale mapping are held. Master trig diagrams (Mtds) on the same sheetlines and scale show the observed rays used to fix the trig stations.

The MCCs, organised by 1:100 000 scale map sheet numbers (½˚ squares – technically not actually square, but normally referred to as such), give current and superseded coordinates for every point that is plotted on the MCDs, with heights (ground level and station mark) and references to the files that contain its coordinates, station descriptions and photo identifications.

Primary triangulation and traverse areas

A small-scale guide to the main areas of primary triangulation and traverse, and of secondary and minor control established by DOS, is provided at the back of the DOS Annual Reports from 1959 to 1984. Individual trig stations and, occasionally, bench marks are plotted, with heights, on DOS 1:125 000 and larger-scale mapping.

International boundary survey data

The international boundary survey data, maps, correspondence and files will be held as a discrete group of records by TNA. It was DOS practice to show international boundaries on the medium-scale mapping wherever the boundaries had been sufficiently well defined and there was enough information available to enable them to be drawn without significant error. The portrayal of boundaries was always agreed with the countries concerned, and correspondence with national survey departments provided additional data. In difficult cases DOS would study the evolution of the boundary over many decades, then write a detailed critique explaining how the boundary alignment was transferred from official documents to the DOS map (for example, the former Yemen Arab Republic-People’s Democratic Republic of Yemen boundary).

DOS map production example set

Four maps have been selected for permanent preservation at TNA as typical examples of DOS map production between 1946 and 1999:

• Series DCS 22, Tanganyika 1:50,000 Sheet 207/111, Preliminary Plot, First Edition 1953.
• Series DOS 419, Sierra Leone 1:50,000 sheet 76, Second Edition–DOS 1967.
• Series DOS 4499P, Belize 1:50,000 Sheet 7 Ambergris Cay, Edition 3–DOS 1980.
• Series YAR 50, Yemen Arab Republic 1:50,000 Sheet 1544C1, Editions 1-DOS 1980 and 2-OSD 1987.

The example map sheets will be held with full supporting records.

DOS staff lists

The DOS staff lists, field party address lists and photographic albums (of map production and field survey processes) will also be at TNA.

Other material

DOS book collection

The DOS book collection was merged with the Ordnance Survey Library’s collection in 1987. It has since been withdrawn from the library and is being relocated to other institutions under the direction of the National Archives. Some of the major holdings were:

• Survey Department Annual Reports
• Land and survey legislation of the Commonwealth.
• Projection tables.
• Gazetteers.
• DOS publications.
• Conference proceedings.
• The Dowson and Sheppard Collection of Cadastral Survey and Land Registration Records, now held by Cambridge University Library.

8mm cine films

Three films showing DOS activities that were worthy of permanent preservation have been transferred to the British Film Institute's National Film and TV Archive. DVD copies of one of these films, a DOS training film, has been supplied to all main repositories holding parts of the Ordnance Survey International Collection.