29-488: North Meadow, Cricklade ( grid reference SU094946 ) is a hay meadow near the town of Cricklade , in Wiltshire , England . It is 24.6 hectares in size. It is a traditionally managed lowland hay-meadow, or lammas land , and is grazed in common between 12 August and 12 February each year, and cut for hay no earlier than 1 July. This pattern of land use and management has existed for many centuries and has resulted in
58-645: A transverse Mercator projection with an origin (the "true" origin) at 49° N , 2° W (an offshore point in the English Channel which lies between the island of Jersey and the French port of St. Malo ). Over the Airy ellipsoid a straight line grid, the National Grid, is placed with a new false origin to eliminate negative numbers, creating a 700 km by 1300 km grid. This false origin
87-504: A grid index where the tens denote the progress from West to East and the units from South to North. In the north of Scotland, the numbering is modified: the 100 km square to the north of 39 is numbered N30; the square to the north of 49 is N40, etc. The grid is based on the OSGB36 datum (Ordnance Survey Great Britain 1936, based on the Airy 1830 ellipsoid ), and was introduced after
116-677: Is a Eurasian species of sedge known as the brown sedge or, in North America , tworank sedge . Carex disticha is native to parts of Northern and Western Europe, where it grows in moist spots in a number of habitat types, and it has been introduced to the Great Lakes region of southern Canada. In its native range, this species is often associated with the Juncus subnodulosus – Cirsium palustre fen-meadow habitat . Carex disticha has also been introduced to Canada , where it
145-485: Is also a rich and diverse insect and reptile fauna present on the site. Typical meadow butterflies include for meadow brown ( Maniola jurtina ), common blue ( Polyommatus icarus ), small heath ( Coenonympha pamphilus ), and the marsh fritillary ( Euphydryas aurinia ). Bordering hedges support gatekeeper ( Pyronia tithonus ), ringlet ( Aphantopus hyperantus ), and speckled wood ( Pararge aegeria ) butterflies. There are also 14 species of dragonfly recorded including
174-629: Is also rich in various herbs including typical hayfield species pepper saxifrage ( Silaum silaus ), yellow rattle ( Rhinanthus minor ), great burnet ( Sanguisorba officinalis ), black knapweed ( Centaurea nigra ), adder's tongue ( Ophioglossum vulgatum ), common meadowrue ( Thalictrum flavum ), and ragged robin ( Lychnis flos-cuculi ). Other meadow flowers include for common knapweed ( Centaurea nigra ), meadow buttercup ( Ranunculus acris ), yellow rattle ( Rhinanthus minor ), cowslip ( Primula veris ), meadowsweet ( Filipendula ulmaria ), and ox-eye daisy ( Leucanthemum vulgare ). The meadow
203-467: Is an abbreviated alphanumeric reference where the letters are simply omitted, e.g. 166712 for the summit of Ben Nevis. Unlike the numeric references described above, this abbreviated grid reference is incomplete; it gives the location relative to an OS 100×100 km square, but does not specify which square. It is often used informally when the context identifies the OS 2-letter square. For example, within
232-621: Is called the Helmert datum transformation , which results in a typical 7 m error from true. The definitive transformation from ETRS89 that is published by the Ordnance Survey is called the National Grid Transformation OSTN15. This models the detailed distortions in the 1936–1962 retriangulation, and achieves backwards compatibility in grid coordinates to sub-metre accuracy. The difference between
261-481: Is located south-west of the Isles of Scilly. In order to minimize the overall scale error, a factor of 2499/2500 is applied. This creates two lines of longitude about 180 km east and west of the central meridian along which the local scale factor equals 1, i.e. map scale is correct. Inside these lines the local scale factor is less than 1, with a minimum of 0.04% too small at the central meridian. Outside these lines
290-650: Is now the preferred coordinate reference system across Ireland. ITM is based on the Universal Transverse Mercator coordinate system (UTM), used to provide grid references for worldwide locations, and this is the system commonly used for the Channel Islands . European-wide agencies also use UTM when mapping locations, or may use the Military Grid Reference System (MGRS), or variants of it. The first letter of
319-606: Is on the west coast of Scotland and the greatest in Kent . These two datums are not both in general use in any one place, but for a point in the English Channel halfway between Dover and Calais , the ED50 longitude lines are about 20 m east of the OSGB36 equivalents, and the ED50 latitude lines are about 150 m south of the OSGB36 ones. Carex disticha Carex disticha
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#1732775981966348-567: Is surrounded by rivers, streams and drainage ditches which add to the biological diversity of the site, with many species of bank-side plant present including for slender tufted-sedge ( Carex acuta ), marsh arrowgrass ( Triglochin palustris ), and great water-dock ( Rumex hydrolapathum ), tubular water-dropwort ( Oenanthe fistulosa ), marsh marigold ( Caltha palustris ), marsh foxtail ( Alopecurus geniculatus ), early marsh-orchid ( Dactylorhiza incarnata ), and brown sedge ( Carex disticha ). As may be expected for such abundant flora, there
377-580: The British Isles : this article describes the system created solely for Great Britain and its outlying islands (including the Isle of Man ). The Irish grid reference system is a similar system created by the Ordnance Survey of Ireland and the Ordnance Survey of Northern Ireland for the island of Ireland. The Irish Transverse Mercator (ITM) coordinate reference system was adopted in 2001 and
406-619: The Churn , and the unique habitat for the fritillary was created by regular winter flooding. Such meadows were once common in Britain, but with the advent of modern farming many were drained and ploughed for arable crops from the 1730s onwards. In the case of North Meadow, it escaped such a fate by virtue of the preservation of the Court Leet , the Saxon system of town governance which made sure
435-755: The retriangulation of 1936–1962 . It replaced the Cassini Grid which had previously been the standard projection for Ordnance Survey maps. The Airy ellipsoid is a regional best fit for Britain; more modern mapping tends to use the GRS80 ellipsoid used by the Global Positioning System (the Airy ellipsoid assumes the Earth to be about 1 km smaller in diameter than the GRS80 ellipsoid, and to be slightly less flattened). The British maps adopt
464-577: The British National Grid is derived from a larger set of 25 squares of size 500 km by 500 km, labelled A to Z, omitting one letter (I) (refer diagram below), previously used as a military grid. Four of these largest squares contain significant land area within Great Britain: S, T, N and H. The O square contains a tiny area of North Yorkshire , Beast Cliff at OV 0000 , almost all of which lies below mean high tide. For
493-588: The OSGB 36 lines in South Cornwall , the difference diminishing to zero in the Scottish Borders , and then increasing to about 50 m north on the north coast of Scotland . (If the lines are further east , then the longitude value of any given point is further west . Similarly, if the lines are further south, the values will give the point a more northerly latitude.) The smallest datum shift
522-709: The OSGB36 National Grid location for Ben Nevis is at 216600, 771200. Grid references may also be quoted as a pair of numbers: eastings then northings in metres, measured from the southwest corner of the SV square. 13 digits may be required for locations in Orkney and further north. For example, the grid reference for Sullom Voe Oil Terminal in the Shetland islands may be given as HU396753 or 439668,1175316 . Another, distinct, form of all-numeric grid reference
551-467: The brown hawker ( Aeshna grandis ), black-tailer skimmer ( Orthetrum cancellatum ) and the ruddy darter ( Sympetrum sanguineum ). The common frog is also prevalent. The meadow also supports a large variety of birds, including great tits , blue tits , common chaffinches , linnets and treecreepers within the bordering hedges; whilst grey wagtails , reed buntings , sedge warblers , barn swallows , sand martins and swifts can be found around
580-433: The context of a location known to be on OS Landranger sheet 41 (which extends from NN000500 in the south-west to NN400900 in the north-east) the abbreviated grid reference 166712 is equivalent to NN166712. If working with more than one Landranger sheet, this may also be given as 41/166712. Alternatively, sometimes numbers instead of the two-letter combinations are used for the 100×100 km squares. The numbering follows
609-570: The coordinates on different datums varies from place to place. The longitude and latitude positions on OSGB 36 are the same as for WGS 84 at a point in the Atlantic Ocean well to the west of Great Britain. In Cornwall , the WGS 84 longitude lines are about 70 metres east of their OSGB 36 equivalents, this value rising gradually to about 120 m east on the east coast of East Anglia . The WGS 84 latitude lines are about 70 m south of
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#1732775981966638-466: The digits is for the first coordinate and the second half for the other. The most common usage is the six figure grid reference , employing three digits in each coordinate to determine a 100 m square. For example, the grid reference of the 100 m square containing the summit of Ben Nevis is NN 166 712 . (Grid references may be written with or without spaces; e.g., also NN166712.) NN has an easting of 200 km and northing of 700 km, so
667-797: The land was held in common. The land is managed by Natural England and is run with the support of the Court Leet . The ancient Hay Lot stones which once marked local farmers' plots can still be seen within the meadow. The meadow was notified as a biological Site of Special Scientific Interest in 1971. Part of the site has been designated a national nature reserve . The site includes for many types of grasses, such as red fescue ( Festuca rubra ), perennial rye grass ( Lolium perenne ), meadow foxtail ( Alopecurus pratensis ), crested dog's tail ( Cynosurus cristatus ), yellow oatgrass ( Trisetum flavescens ), meadow brome ( Bromus commutatus ), and meadow barley ( Hordeum brachyantherum ). The meadow
696-473: The local scale factor is greater than 1, and is about 0.04% too large near the east and west coasts. Grid north and true north are only aligned on the central meridian (400 km easting) of the grid which is 2° W (OSGB36) and approx. 2° 0′ 5″ W ( WGS 84 ). A geodetic transformation between OSGB 36 and other terrestrial reference systems (like ITRF2000 , ETRS89 , or WGS 84 ) can become quite tedious if attempted manually. The most common transformation
725-572: The origin (0, 0), which lies to the west of the Isles of Scilly . The Ordnance Survey (OS) devised the national grid reference system, and it is heavily used in its 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. A number of different systems exist that can provide grid references for locations within
754-523: The rivers and ditches. 51°39′00″N 1°51′56″W / 51.65012°N 1.86553°W / 51.65012; -1.86553 Ordnance Survey National Grid 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
783-440: The second letter, each 500 km square is subdivided into 25 squares of size 100 km by 100 km, each with a letter code from A to Z (again omitting I) starting with A in the north-west corner to Z in the south-east corner. These squares are outlined in light grey on the "100km squares" map, with those containing land lettered. The central (2° W) meridian is shown in red. Within each square, eastings and northings from
812-412: The south west corner of the square are given numerically. For example, NH0325 means a 1 km square whose south-west corner is 3 km east and 25 km north from the south-west corner of square NH. A location can be indicated to varying resolutions numerically, usually from two digits in each coordinate (for a 1 km square) through to five (for a 1 m square); in each case the first half of
841-518: The species rich grassland flora and fauna present on the site. Over 250 species of higher plant occur in the meadow, but it is of particular note as it holds by far the largest British population of the snake's-head fritillary ( Fritillaria meleagris ). The 500,000 fritillaries which flower each year represent 80% of the British population. The meadow is situated between two rivers, the Thames and
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