The dates in brackets after the name of each map series indicate, as far as can be determined, the date of first publication and the date of last revision respectively.

1-inch scale:

• 1-inch ‘Old Series’ (1805 - c1875?)
  The ‘Triangulation of Great Britain’ had begun around 1784, at the request of King George III, who was fearful of French invasion. The survey was initally carried out by the Board of Ordnance (the precursor to the Ministry of Defence), but the separate entity of the Ordnance Survey was established in 1791. The very first 1-inch map made by the Ordnance Survey was published privately in 1801, and covered part of Kent. It was nicknamed the ‘Mudge’ map, after the then Director General of the Ordnance Survey.
  The first numbered sheet of the official series was published in 1805. The series was laid out on 110 ‘sheets’ covering England & Wales, but was published (between 1805 and 1874) in 263 sheets (some sheets were split into quarter sheets). The sheet lines are largely irregular, due to there being no single standard projection or origin for the whole series. However, later sheets (north of a line between Preston-Hull) used the Cassini projection on the origin of Delamere Forest (a triangulation point in Cheshire). This new projection and origin was to form the basis for Ordnance Survey map sheet lines until the 1940s.
  Survey work for the Old series carried on until 1869, each new map being engraved as soon as possible after the survey work was completed. During this time of great technological advance, and particularly with new railways being built at an astonishing rate, it was necessary to update the sheets after they had been first published. With some reprints, the state of the railways is the only way to determine the revision date of the map, as the original publication date were often left unaltered on revision.
  After the introduction of the ‘New Series’ in 1874, this series became known as the ‘Old Series’.

• 1-inch New Series (1874 - c.1897?)
  This series was the first to be constructed on a single, standard projection and origin (Cassini projection, origin Delamere Forest triangluation point, Cheshire). It was laid out to cover England & Wales in 360 sheets, each 18 miles × 12 miles, with no overlaps. In practice, it was found more desirable to combine some sheets, particularly around the coastal areas, and this led to some irregular-sized sheets. Thus the sheet total was reduced to 349, of which 340 sheets were published, between 1874 and 1896. Sheets 1-73 were re-numbered re-issues of ‘Old Series’ sheets north of a line between Preston and Hull. Survey work for the series was carried out between 1842 and 1893.

• 1-inch Revised New Series (1895 - c.1906?)
  The ‘First National Revision’ was carried out between 1893 and 1898, and yielded a revised series of 1-inch sheets. 356 of the 360 as laid-out were covered, combined into 346 separate sheets, first published between 1895 and 1899. A few sheets were combined still further on re-issue.

• 1-inch Revised New Series in colour (1897 - c.1906?)
  Further combination of some sheets meant that 289 separate sheets, covering 351 of the originally laid-out 360, were published for the colour printings of the Revised New Series. This was the first series to be printed in multi-colour form.

• 1-inch Third Edition [Small Sheet Series] (1903 - 1913)
  This series was surveyed from 1901-1912, and published in 347 sheets between 1903 and 1913, with later reprints and revisions. The sheet lines matched those of the New Series. After the introduction of the ‘Large Sheet Series’ of the Third Edition, this series was given its ‘Small Sheet Series’ tag.

• 1-inch Third Edition [Small Sheet Series, in colour] (1903 - 1909)
  96 sheets from the Third Edition [Small Sheet Series] were updated with multi-colour printing. This series was discontinued after the introduction of the ‘Large Sheet Series’ of the Third Edition, and this series was given its ‘Small Sheet Series’ tag.

• 1-inch Third Edition [Large Sheet Series] (1907 - 1923)
  Surveyed from 1901-1912, this series was published between 1907 and 1913, with later reprints and revisions. The 152 sheets of this series, all printed in multi-colour format, were re-cast from the original Third Edition sheets.

• 1-inch Fourth Edition (1911 - 1912)
  This was a series of small-format sheets. It was extremely short-lived - only 7 sheets covering eastern Kent were published before the series was discontinued in favour of the Popular Edition.

• 1-inch Popular Edition (1919 - 1940)
  The survey for this series was between 1912 and 1923; publication was between 1919 and 1926, with later reprints and revisions. The series consisted of 146 large-format sheets, printed in 7 colours. Most sheets covered an area approximately 27 miles × 18 miles, with a few exceptions. The Popular Edition was designed to appeal to a wide range of users including motorists, cyclists and tourists - hence the ‘Popular’ tag. This series is often mistakenly referred to as the Fourth Edition, because of that series’ early demise.

• 1-inch Fifth Edition (1931 - 1940)
  Survey work on this series was carried out between 1928 and 1936. The original sheet lines were slightly modified from the Popular Edition to use the new National Yard Grid. This was a precursor to the National Grid in use today - using the same projection (Transverse Mercator) and with the origin at 49°N, 2°W. Unlike the modern National Grid, however, it used yards instead of metres; the grid lines on the map were 5,000 yards apart. Most sheets covered an area approximately 29½ miles × 18¼ miles, or 29½ miles × 23¾ miles, with a few deviations.
  The intention of the series was to create a map that showed the relief of the terrain more clearly than with contour lines alone. Thus, in 1931, the ‘Fifth (Relief) Edition’ came into being. It used varied brown shading to indicate areas of different altitude. Unfortunately some critics levelled the accusation that it appeared “mud-coloured”, and sales of the map were sluggish. In 1934, it was decided to do an ‘about-turn’, and produce a standard edition without the relief detail - simply called the ‘Fifth Edition’. Sales picked up and the series looked on course to be successful; by 1936 the last ‘Fifth (Relief) Edition’ sheet had been published. Meanwhile, in 1935, the pace of publication of the series was deemed to be too slow, and the sheet lines were reviewed. It was decided to increase the sheet size to approximately 35¼ miles × 26¾ miles, or 38 miles × 26¾ miles, with a few deviations. For the area of southwest England west of Wellington (Somerset) and Ottery St Mary (Devon), and also for a few sheets around London, the original sheet size was retained. Each extended sheet was numbered the same as its nearest sheet in the originally-proposed, smaller sheet series. This created gaps in the numbering of the sheets which would have looked decidedly odd had the series been completed.
  In 1935, an investigative committee was set up under the command of Sir John Davidson to recommend how Ordnance Survey mapping could be improved. In the years that followed, one of the more important recommendations was that a kilometre-based national grid should be introduced. For Ordnance Survey, this meant there was a way out of the now rather messy Fifth Edition, and it was decided the series should be discontinued. Only 38 sheets, covering most of Southern England south of Saffron Walden, had been published (some overlapping sheets around the London area). The last sheet was updated in 1940.

• 1-inch War Revisions (1940 - 1945)
  Two nights of bombing in Southampton at the beginning of December 1940 led to the destruction of several printed maps, and also several glass negatives, on which the printing plates were based. Printing work on the New Popular Edition had begun, but Ordnance Survey had difficulty persuading the War Office to allow these first sheets to be published, as it was felt the risk of troops being confused by the differing grid systems was too great. Thus, Ordnance Survey were forced to use their surviving printing plates to create a set of War Revisions, mostly based on Popular Edition sheet lines, and mostly incorporating a military grid based on the earlier Cassini projection. Initially these War Revisions were issued only for military consumption, however in 1942 a decision was made to sell them to the general public.

• 1-inch New Popular (Sixth) Edition (1945 - 1959)
  Work on this series had originally started in 1939. The work was disrupted almost immediately by World War 2, but a very speedy publication programme began in 1945. After the abandonment of the Fifth Edition, the ‘Fourth National Revision’ of 1-inch mapping (on which the Fifth Edition was based) was also abandoned in May 1940, apparently because of ‘unspecified difficulties encountered by the revisers’. The New Popular Edition used the latest revision material available, thus the style was identical to that of the Fifth Edition in the parts of the country that series covered, but was identical to that of the Popular Edition in the other parts of the country. The series was originally intended to cover England, Wales and Scotland in 190 sheets. However, again seemingly due to the pressures of the War years, the sheets for Scotland were never introduced and only 115 sheets were published. The sheets used the new kilometre-based National Grid, on the Transverse Mercator projection, by recommendation of the “Davidson Committee”. Each map covered an area of 40km × 45km.

• 1-inch Seventh Series (1952 - 1974)
  A new, clearer-style 1-inch map was created for the slowly-recovering post-war Britain. A pilot sheet, covering Hereford, was produced in 1949, and the publication of the full national series began in 1952. This was the first series to cover Great Britain in a single series of sheets. An important innovation came in 1960, when Public Rights of Way were first included on the maps. The sheet lines matched those of the New Popular Edition (where published), and covered Britain in 190 sheets. In December 1965, this was reduced to 189 sheets by the combination of sheets 138 (Fishguard) and 151 (Pembroke) into one large sheet.

1:50 000 scale:

• 1:50 000 First Series (1974 - 1985)
  In 1964, the Ordnance Survey made the decision to complete the move to entirely metric mapping. After several trials of many different formats, a scale of 1:50 000 was chosen. This first series of 1:50 000 maps was created by photographically enlarging the latest editions of the 1-inch Seventh Series, and incorporating minor revisions. Several colour changes were also introduced: motorways were changed from red to blue, built-up areas from grey to stippled orange, and several other less significant changes. Sheet lines were redrawn, mapping Britain in 204 sheets, each map covering an area of 40km × 40km.

• 1:50 000 Second Series (1974 - present)
  These are redrawn versions of the 1:50 000 First Series, on the same sheet lines. Originally the sheets started out with the same colour scheme as the 1:50 000 First Series, but around 1981 the colour of main roads was changed from red to dark magenta. Throughout its life, this series has been updated with a large amount of tourist information, making it very popular. From 2000, the specification of the sheets was changed slightly, bringing about minor changes to some map symbols. These included changing the colour of primary routes from dark magenta to green, and making bolder the marking of areas owned by the National Trust or the Forestry Commission.

1:25 000 scale:

• 1:25 000 First Series (1945 - 1986)
  1:25 000 mapping had been used by the military since the First World War, and another of the recommendations of the Davidson Committee was that a national series of 1:25 000 maps should be published in a civilian edition, mainly to fill a gap in the market between 1-inch (1:63 360) and 6-inch (1:10 560) mapping. Publication of the series began in 1945, under the title ‘Provisional Edition’. The intention was to eventually replace the ‘Provisional Edition’ with a ‘Regular Edition’ of improved specification, however only 11 sheets became ‘Regular Edition’, covering an area round Plymouth, first published in 1956. Most of Great Britain was covered; only the highlands and islands of Scotland were left out. Most sheets covered an area of 10km × 10km (some sheets were extended by up to 5km, on the coasts), and were numbered according to their position on the National Grid. In practice, the small coverage area of each sheet and the rigid grid-based sheet lines meant that the public reaction to the new series was decidedly mixed. Sales were slow to pick up, and the discontinuation of the series was seriously considered on more than one occasion. Walkers, in particular, said that a larger sheet size would be beneficial, and a new sheet layout was trialled: each sheet would be 20km × 15km, the sheets would be consecutively numbered. However by the time the first of these large sheets (designated the ‘1:25 000 Second Series (Provisional Edition)’) went on sale in 1960, complaints about the increased sheet size, particularly from teachers who felt the original size was ideal for school desks, forced the OS to rethink the plan. In February 1962, a sheet size of 20km × 10km was formally decided upon for the Second Series. After the Second Series began production later in the 1960s, the First Series was continued with only very minimal revision. The last batch of three updated First Series sheets were published in June 1986, and the series was finally completely replaced in 1989.

• 1:25 000 Second Series (1965 - 1996)
  After the wrangling over sheet sizes was (temporarily) resolved in February 1962, work was put in hand immediately on producing a pilot sheet for the Second Series. This was completed by March 1963, and the first 14 sheets of the full series were published in December 1965. These maps were produced to a much improved specification, most importantly including quickly-recognisable symbols for public rights of way. The standard sheet size of 20km × 10km (varied slightly around the coasts) was widely welcomed, particularly by ramblers’ groups. The full series consisted of almost 1,400 sheets. Even this series didn’t get an easy ride, though: a proposal for a change to 20km × 20km sheets was considered in 1969, and in 1973 the possibilty of abandoning it was also considered, but rejected later the same year after public complaints. And to add to the woes, the speed of publication of new sheets in the series was, to some, painfully slow. Gaps of 20 years or more often occurred between even the latest revised reprint of a First Series sheet and its first Second Series replacement. In 1979, the series was given the ‘Pathfinder’ tag, to go along with the ‘Landranger’ tag of the 1:50 000 series. This recognised the 1:25 000’s popularity with walkers. At first, the sheet numbering followed a similar method to the First Series sheets, relating to the National Grid. However, from the mid-1980s, the series was given consecutive numbers from North to South. At the same time, it was decided to discontinue or abandon any ‘Pathfinder’ sheets wholly underlying Outdoor Leisure maps. The series was finally completed in December 1989. The troubles were not over yet, however: Certain sections of the public still demanded larger sheet sizes, and in 1992 two ‘Pathfinder’ sheets were joined together to cover the Gower in a single sheet. This experiment was successful and spawned the early sheets of the ‘Explorer’ series. The last updated Second Series sheet was published around 1996 and, after a gap of a year or so, publication of the national Explorer series began.

• 1:25 000 ‘Outdoor Leisure’ Series (1972 - 2000)
  This series was designed to allow single sheets to cover areas popular with tourists, particularly walkers, where previously several sheets of the 1:25 000 First or Second Series would have been needed. They used the latest available revisions of either the First or Second Series sheets for each area, with the addition of information of interest to tourists. The first sheet, ‘The Dark Peak’, was published in 1972 and covered part of the Peak District. Over the 28 years that the series was in existance in its own right, the number of sheets in the series grew steadily. Some sheets were discontinued, leading to gaps in the numbering of the sheets. The last sheet to be created was Sheet 45, ‘The Cotswolds’, in 1998. The last updated sheet was published in 2000, and 2 years later the series was integrated with the ‘Explorer’ series.

• 1:25 000 ‘Explorer’ Series (1994 - present)
  Between March 1994 and May 1997, 31 ‘Explorer’ sheets covering ‘popular beauty spots’ were published on an experimental basis, to complement the ‘Outdoor Leisure’ series which covered more popular areas. The first 5 of these used the same simple colour scheme as the 1:25 000 Second Series sheets on which they were based: roads in orange (2 shades thereof) or uncoloured, rivers in blue, and forests & rights of way in green. The later sheets (nos. 6-31, published from April 1995) used full-colour printing, making differing types of roads a great deal easier to identify: motorways in blue, A-roads in red, B-roads in orange, unclassified roads in yellow (2 shades thereof) or uncoloured, and forests & rights of way in green.
  Following the success of the initial 31 experimental sheets, it was decided a full national series of full-colour ‘Explorer’ sheets should be produced, to cover all areas of the country not covered by the ‘Outdoor Leisure’ series, and thus to replace the 1:25 000 Second Series. The first sheet in the extended series was published in May 1997. The extension of the series led to the renumbering and some recasting of the original Explorer sheets (nos. 1 to 31), which took place over the following 4¾ years, concurrent with the publication of several new sheets. Geographically-based sheet lines were used instead of purely grid-based sheet lines, in much the same way as the layout of the 1:50 000 sheets was created. This was designed to make the Explorer series more user-friendly and therefore, hopefully, more popular than the previous national 1:25 000 series. New techniques, such as digital scanning, were employed to ensure publication of new sheets at a much faster rate than before. This meant that coverage of the whole of Great Britain was complete by March 2003.
  The 370 standard sheets are numbered (slightly haphazardly) from South to North, the first sheet being no. 101. In 2002, the series was integrated with the ‘Outdoor Leisure’ series. These 33 ‘Explorer OL’ sheets carry their original numbers from the ‘Outdoor Leisure’ series. Sheet lines are not regular, and the area that each sheet covers is not uniform, though generally an Explorer sheet covers approximately 600km² - 700km². Some sheets are printed double-sided, thus increasing the area each map can cover.
  The series is currently undergoing an 18-month whole-series revision programme to show new areas of ‘Access Land’ (areas of land upon which the public are permitted to ‘roam’), following creation of such areas under the Countryside & Rights of Way Act 2000. Publication of these sheets has be timed to approximately co-incide with the introduction of the new rights in each of 9 regions of England & Wales (it is not yet known how the sheets for Scotland will be revised). The sheets with the new specification are re-named ‘OS Explorer’ sheets upon publication.