Ordnance Survey in the context of "Firth"

The Somerset Levels are a coastal plain and wetland area of Somerset, England, running south from the Mendips to the Blackdown Hills.

The Somerset Levels have an area of about 160,000 acres (650 km) and are bisected by the Polden Hills; the areas to the south are drained by the River Parrett, and the areas to the north by the rivers Axe and Brue. The Mendip Hills separate the Somerset Levels from the North Somerset Levels. The Somerset Levels consist of marine clay "levels" along the coast and inland peat-based "moors"; agriculturally, about 70 per cent is used as grassland and the rest is arable. Willow and teazel are grown commercially and peat is extracted.

The Permanent Committee on Geographical Names (PCGN) is an independent inter-departmental body in the United Kingdom established in 1919. Its function is to establish standard names for places outside the UK, for the use of the British government. The Committee has collaborated with the Foreign Names Committee of the United States Board on Geographic Names to agree a joint romanization system, first published in 1994 as the Romanization Systems and Roman-Script Spelling Conventions.

The members of the PCGN are: British Broadcasting Corporation Monitoring Service, Intelligence Collection Group (ICG) (formerly Defence Geospatial Intelligence), Defence Intelligence Staff, Foreign and Commonwealth Office, Government Communications Headquarters, Hydrographic Office, Ordnance Survey, Royal Geographical Society and Royal Scottish Geographical Society.

Edington is a village and civil parish in Wiltshire, England, about 4 miles (6 km) east-northeast of Westbury. The village lies under the north slope of Salisbury Plain and the parish extends south onto the Plain. Its Grade I listed parish church was built for Edington Priory in the 14th century.

Tinhead is the former name of the eastern half of present-day Edington, towards Coulston along the B3098 Westbury to Market Lavington road. Tinhead is labelled on the Ordnance Survey map of 1945 but not on the 1958 map. Today the combined settlement is Edington and the name survives only in Tinhead Hill and Tinhead Lane.

Chromolithography is a method for making multi-colour prints in lithography, and in theory includes all types of lithography that are printed in colour. However, in modern usage it is normally restricted to 19th-century works, and the higher quality examples from that period; almost all 21st-century colour printing uses lithography, but would not be described using the term chromolithography. When chromolithography is used to reproduce photographs, the term photochrome is frequently used. Lithography is a method of printing on flat surfaces using a flat printing plate instead of raised relief or recessed intaglio techniques.

Chromolithography became the most successful of several methods of colour printing developed in the 19th century. Other methods were developed by printers such as Jacob Christoph Le Blon, George Baxter and Edmund Evans, and mostly relied on using several woodblocks with different colours. Hand-colouring also remained important. For example, elements of the official British Ordnance Survey maps were coloured by hand by boys until 1875. The initial chromolithographic technique involved the use of multiple lithographic stones, one for each colour, and was still extremely expensive when done for the best quality results. Depending on the number of colours present, a chromolithograph could take even very skilled workers months to produce.

An ayre is the name used for shingle beaches found in Orkney, Shetland, the Isle of Man, Lancashire, Cumbria and Northumbria. The word is derived from the Old Norse eyrr, meaning a shingle beach or gravelly place, and may be applied to ordinary beaches, cliff-foot beaches such as the Lang Ayre in Northmavine, Shetland, spits, bars or tombolos, but only if formed of shingle.

More than 130 such shingle beaches are named on Ordnance Survey maps of Shetland, but far fewer in Orkney, where most beaches are formed of sand. The word in its Old Norse form is common in Iceland, and it also occurs in a few place names in the north and west of the Scottish mainland which had a strong Norse influence, such as Eriboll ("a homestead on a shingle beach") and in the names of several shingle banks—Salt Ayre, Green Ayre, Stake Ayre, Rabbit Ayre and Whinny Ayre—in the tidal reach of the River Lune at Lancaster.

OpenStreetMap (OSM) is a map database maintained by a community of volunteers via open collaboration. Contributors collect data from surveys, trace from aerial photo imagery or satellite imagery, and import from other freely licensed geodata sources. OpenStreetMap is freely licensed under the Open Database License and is commonly used to make electronic maps, inform turn-by-turn navigation, and assist in humanitarian aid and data visualisation. OpenStreetMap uses its own data model to store geographical features which can then be exported into other GIS file formats. The OpenStreetMap website itself is an online map, geodata search engine, and editor.

OpenStreetMap was created by Steve Coast in response to the Ordnance Survey, the United Kingdom's national mapping agency, failing to release its data to the public under free licences in 2004. Initially, maps in OSM were created only via GPS traces, but it was quickly populated by importing public domain geographical data such as the U.S. TIGER and by tracing imagery as permitted by source. OpenStreetMap's adoption was accelerated by the development of supporting software and applications and Google Maps' 2012 introduction of pricing.

The term benchmark, bench mark, or survey benchmark originates from the chiseled horizontal marks that surveyors made in stone structures, into which an angle iron could be placed to form a "bench" for a leveling rod, thus ensuring that a leveling rod could be accurately repositioned in the same place in the future. These marks were usually indicated with a chiseled arrow – specifically a broad arrow – below the horizontal line. A benchmark is a type of survey marker.

The term is generally applied to any item used to mark a point as an elevation reference. Frequently, bronze or aluminum disks are set in stone or concrete, or on rods driven deeply into the earth to provide a stable elevation point. If an elevation is marked on a map, but there is no physical mark on the ground, it is a spot height.

The Ordnance Survey National Grid reference system (OSGB), also known as British National Grid (BNG), is a system of geographic grid references, distinct from latitude and longitude, whereby any location in Great Britain can be described in terms of its distance from the origin (0, 0), which lies to the west of the Isles of Scilly.

Devised by the Ordnance Survey (OS), the national grid reference system is heavily used in OS survey data and in maps based on those surveys, whether published by the Ordnance Survey or by commercial map producers. Grid references are also commonly quoted in other publications and data sources, such as guide books and government planning documents.