1.
Ordnance Survey
–
Ordnance Survey is a non-ministerial government department which acts as the national mapping agency for Great Britain and is one of the worlds largest producers of maps. Since 1 April 2015 it has operated as Ordnance Survey Ltd, the Ordnance Survey Board remain accountable to the Secretary of State for Business, Energy and Industrial Strategy. It is also a member of the Public Data Group, the agencys name indicates its original military purpose, mapping Scotland in the wake of the Jacobite rebellion in 1745. There was also a general and nationwide need in light of the potential threat of invasion during the Napoleonic Wars. Ordnance Survey mapping is usually classified as either large-scale or small-scale, the Surveys large-scale mapping comprises maps at six inches to the mile or more and was available as sheets until the 1980s, when it was digitised. Small-scale mapping comprises maps at less than six inches to the mile, such as the one inch to the mile leisure maps. These are still available in sheet form. Ordnance Survey maps remain in copyright for fifty years after their publication, some of the Copyright Libraries hold complete or near-complete collections of pre-digital OS mapping. The origins of the Ordnance Survey lie in the aftermath of the last Jacobite rising which was defeated by forces loyal to the government at the Battle of Culloden in 1746. In 1747, Lieutenant-colonel David Watson proposed the compilation of a map of the Highlands to facilitate the subjugation of clans, in response, King George II charged Watson with making a military survey of the Highlands under the command of the Duke of Cumberland. Among Watsons assistants were William Roy, Paul Sandby and John Manson, the survey was produced at a scale of 1 inch to 1000 yards and included the Duke of Cumberlands Map now held in the British Library. This work was the point of the Principal Triangulation of Great Britain. Roys technical skills and leadership set the standard for which Ordnance Survey became known. Work was begun in earnest in 1790 under Roys supervision, when the Board of Ordnance began a military survey starting with the south coast of England. A set of stamps, featuring maps of the Kentish village of Hamstreet, was issued in 1991 to mark the bicentenary. In 1801, the first one-inch-to-the-mile map was published, detailing the county of Kent, during the next twenty years, roughly a third of England and Wales was mapped at the same scale under the direction of William Mudge, as other military matters took precedence. It took until 1823 to re-establish a relationship with the French survey made by Roy in 1787, by 1810, one inch to the mile maps of most of the south of England were completed, but were withdrawn from sale between 1811 and 1816 because of security fears. It was gruelling work, major Thomas Colby, later the longest serving director general of Ordnance Survey, in 1824, Colby and most of his staff moved to Ireland to work on a six-inches-to-the-mile valuation survey
2.
Surveying
–
Surveying or land surveying is the technique, profession, and science of determining the terrestrial or three-dimensional position of points and the distances and angles between them. A land surveying professional is called a land surveyor, Surveyors work with elements of geometry, trigonometry, regression analysis, physics, engineering, metrology, programming languages and the law. Surveying has been an element in the development of the environment since the beginning of recorded history. The planning and execution of most forms of construction require it and it is also used in transport, communications, mapping, and the definition of legal boundaries for land ownership. It is an important tool for research in other scientific disciplines. Basic surveyance has occurred since humans built the first large structures, the prehistoric monument at Stonehenge was set out by prehistoric surveyors using peg and rope geometry. In ancient Egypt, a rope stretcher would use simple geometry to re-establish boundaries after the floods of the Nile River. The almost perfect squareness and north-south orientation of the Great Pyramid of Giza, built c.2700 BC, the Groma instrument originated in Mesopotamia. The mathematician Liu Hui described ways of measuring distant objects in his work Haidao Suanjing or The Sea Island Mathematical Manual, the Romans recognized land surveyors as a profession. They established the basic measurements under which the Roman Empire was divided, Roman surveyors were known as Gromatici. In medieval Europe, beating the bounds maintained the boundaries of a village or parish and this was the practice of gathering a group of residents and walking around the parish or village to establish a communal memory of the boundaries. Young boys were included to ensure the memory lasted as long as possible, in England, William the Conqueror commissioned the Domesday Book in 1086. It recorded the names of all the owners, the area of land they owned, the quality of the land. It did not include maps showing exact locations, abel Foullon described a plane table in 1551, but it is thought that the instrument was in use earlier as his description is of a developed instrument. Gunters chain was introduced in 1620 by English mathematician Edmund Gunter and it enabled plots of land to be accurately surveyed and plotted for legal and commercial purposes. Leonard Digges described a Theodolite that measured horizontal angles in his book A geometric practice named Pantometria, joshua Habermel created a theodolite with a compass and tripod in 1576. Johnathon Sission was the first to incorporate a telescope on a theodolite in 1725, in the 18th century, modern techniques and instruments for surveying began to be used. Jesse Ramsden introduced the first precision theodolite in 1787 and it was an instrument for measuring angles in the horizontal and vertical planes
3.
Level staff
–
It cannot be used without a leveling instrument. Levelling rods can be one piece, but many are sectional and can be shortened for storage, there are many types of rods, with names that identify the form of the graduations and other characteristics. Markings can be in imperial or metric units, some rods are graduated on one side only while others are marked on both sides. If marked on both sides, the markings can be identical or can have imperial units on one side, in the photograph on the right, both a metric and imperial levelling rod are seen. This is an aluminum rod, coated white with markings in contrasting colours. The imperial side has a yellow background. The metric rod has major numbered graduations in meters and tenths of meters, between the major marks are either a pattern of squares and spaces in different colours or an E shape with horizontal components and spaces between of equal size. In both parts of the pattern, the squares, lines or spaces are precisely one centimetre high. When viewed through a telescope, the observer can easily visually interpolate a 1 cm mark to a quarter of its height. Usually readings are interpolated to mm, on this side of the rod, the colours of the markings alternate between red and black with each meter of length. The imperial graduations are in feet, tenths of a foot, the tenths of a foot point is indicated by the top of the long mark with the upward sloped end. The point halfway between tenths of a foot marks is indicated by the bottom of a medium length black mark with a sloped end. Each mark or space is approximately 3mm, yielding roughly the same accuracy as the metric rod, rods come in two classes, Self-reading rods. Self-reading rods are rods that are read by the person viewing the rod through the telescope of the instrument, the graduations are sufficiently clear to read with good accuracy. Target rods, on the hand, are equipped with a target. The target is a round or oval plate marked in quarters in contrasting colours such as red, a hole in the centre allows the instrument user to see the rods scale. The target is adjusted by the according to the instructions from the instrument man. When the target is set to align with the crosshairs of the instrument, the target may have a vernier to allow fractional increments of the graduation to be read
4.
Broad arrow
–
A broad arrow is a type of arrow with a typically flat barbed head. It is a symbol used traditionally in heraldry, most notably in England, the broad arrow as a heraldic device has two tapering blades, known as barbs. When these barbs are engrailed on the inside, it is called a pheon, parkers A Glossary of Terms Used in Heraldry states, A broad arrow differs somewhat. And resembles a pheon, except in the omission of the edge on the inside of the barbs. The pheon, the broad arrow, occurs in heraldry in the arms of the Sidney and Coates families. The colleges newsletter for alumni is also called Pheon, the Pheon also appears in the arms of Hampden-Sydney College. The Office of Ordnance was created by Henry VIII in 1544 and it became the Board of Ordnance in 1597, its principal duties being to supply guns, ammunition, stores and equipment to the Kings Navy. The Office and Board used the arrow to signify at first objects purchased from the monarchs money. The introduction of this symbol is attributed to Sir Philip Sidney, Joint Master of the Ordnance in 1585/6, the broad arrow marks were also used by Commonwealth countries on their ordnance. With the demise of the Board in 1855, the War Department, similarly to hallmarks, it is currently a criminal offence in the United Kingdom to reproduce the broad arrow without authority. Section 4 of the Public Stores Act 1875 makes it illegal to use the arrow on any goods without permission. The broad arrow was used by the British to mark trees intended for ship building use in North America during colonial times, three axe strikes, resembling an arrowhead and shaft, were marked on large mast-grade trees. We. forbid all persons whatsoever from felling, cutting or destroying any such trees without the license from us. Initially England imported its mast trees from the Baltic states, but it was an expensive, lengthy, much of British naval policy at the time revolved around keeping the trade route to the Baltics open. With Baltic timber becoming less appealing to use, the Admiraltys eye turned towards the Colonies, colonists paid little attention to the Charters Mast Preservation Clause, and tree harvesting increased with disregard for broad arrow protected trees. However, as Baltic imports decreased, the British timber trade increasingly depended on North American trees and this process was open to abuse, and the British monopoly was very unpopular with colonists. Part of the reason was that many protected trees were on either town-owned or privately owned lands, colonists could only sell mast trees to the British, but were substantially underpaid for the lumber. Even though it was illegal for the colonists to sell to enemies of the crown, acts of Parliament in 1711,1722 and 1772 extended protection finally to 12-inch-diameter trees and resulted in the Pine Tree Riot that same year
5.
Height
–
Height is the measure of vertical distance, either how tall something is, or how high up it is. For example The height of the building is 50 m or The height of the airplane is 10,000 m, when used to describe how high something like an airplane or mountain peak is from sea level, height is more often called altitude. Height is measured along the axis between a specified point and another. English high is derived from Old English hēah, ultimately from Proto-Germanic *xauxa-z, the derived noun height, also the obsolete forms heighth and highth, is from Old English híehþo, later héahþu, as it were from Proto-Germanic *xaux-iþa. In elementary models of space, height may indicate the third dimension, height is normal to the plane formed by the length and width. Height is also used as a name for more abstract definitions. Although height is relative to a plane of reference, most measurements of height in the world are based upon a zero surface. Both altitude and elevation, two synonyms for height, are defined as the position of a point above the mean sea level. One can extend the surface under the continents, naively. In practice, the sea level under a continent has to be computed from gravity measurements, instead of using the sea level, geodesists often prefer to define height from the surface of a reference ellipsoid, see Geodetic system, vertical datum. Defining the height of geographic landmarks becomes a question of reference, in aviation terminology, the terms height, altitude, and elevation are not synonyms. Usually, the altitude of an aircraft is measured from sea level, Elevation is also measured from sea level, but is most often regarded as a property of the ground. Thus, elevation plus height can equal altitude, but the term altitude has several meanings in aviation, Human height is one of the areas of study within anthropometry. While height variations within a population are largely genetic, height variations between populations are mostly environmental, the United Nations uses height to monitor changes in the nutrition of developing nations. In human populations, average height can distill down complex data about the birth, upbringing, social class, diet. Acrophobia Centimetre–gram–second system of units Chinese units of measurement Elevation Human height Imperial units International System of Units United States customary units
6.
Sea level
–
Mean sea level is an average level of the surface of one or more of Earths oceans from which heights such as elevations may be measured. A common and relatively straightforward mean sea-level standard is the midpoint between a low and mean high tide at a particular location. Sea levels can be affected by factors and are known to have varied greatly over geological time scales. The careful measurement of variations in MSL can offer insights into ongoing climate change, the term above sea level generally refers to above mean sea level. Precise determination of a sea level is a difficult problem because of the many factors that affect sea level. Sea level varies quite a lot on several scales of time and this is because the sea is in constant motion, affected by the tides, wind, atmospheric pressure, local gravitational differences, temperature, salinity and so forth. The easiest way this may be calculated is by selecting a location and calculating the mean sea level at that point, for example, a period of 19 years of hourly level observations may be averaged and used to determine the mean sea level at some measurement point. One measures the values of MSL in respect to the land, hence a change in MSL can result from a real change in sea level, or from a change in the height of the land on which the tide gauge operates. In the UK, the Ordnance Datum is the sea level measured at Newlyn in Cornwall between 1915 and 1921. Prior to 1921, the datum was MSL at the Victoria Dock, in Hong Kong, mPD is a surveying term meaning metres above Principal Datum and refers to height of 1. 230m below the average sea level. In France, the Marégraphe in Marseilles measures continuously the sea level since 1883 and it is used for a part of continental Europe and main part of Africa as official sea level. Elsewhere in Europe vertical elevation references are made to the Amsterdam Peil elevation, satellite altimeters have been making precise measurements of sea level since the launch of TOPEX/Poseidon in 1992. A joint mission of NASA and CNES, TOPEX/Poseidon was followed by Jason-1 in 2001, height above mean sea level is the elevation or altitude of an object, relative to the average sea level datum. It is also used in aviation, where some heights are recorded and reported with respect to sea level, and in the atmospheric sciences. An alternative is to base height measurements on an ellipsoid of the entire Earth, in aviation, the ellipsoid known as World Geodetic System 84 is increasingly used to define heights, however, differences up to 100 metres exist between this ellipsoid height and mean tidal height. The alternative is to use a vertical datum such as NAVD88. When referring to geographic features such as mountains on a topographic map, the elevation of a mountain denotes the highest point or summit and is typically illustrated as a small circle on a topographic map with the AMSL height shown in metres, feet or both. In the rare case that a location is below sea level, for one such case, see Amsterdam Airport Schiphol
7.
Geoid
–
The geoid is the shape that the surface of the oceans would take under the influence of Earths gravity and rotation alone, in the absence of other influences such as winds and tides. This surface is extended through the continents, all points on a geoid surface have the same gravity potential energy. The geoid can be defined at any value of gravitational potential such as within the earths crust or far out in space and it does not correspond to the actual surface of Earths crust, but to a surface which can only be known through extensive gravitational measurements and calculations. It is often described as the true figure of the Earth. The surface of the geoid is higher than the reference ellipsoid wherever there is a gravity anomaly. The geoid surface is irregular, unlike the ellipsoid which is a mathematical idealized representation of the physical Earth. Although the physical Earth has excursions of +8,848 m and −429 m, If the ocean surface were isopycnic and undisturbed by tides, currents, or weather, it would closely approximate the geoid. The permanent deviation between the geoid and mean sea level is called ocean surface topography, If the continental land masses were criss-crossed by a series of tunnels or canals, the sea level in these canals would also very nearly coincide with the geoid. This means that when traveling by ship, one does not notice the undulations of the geoid, the vertical is always perpendicular to the geoid. Likewise, spirit levels will always be parallel to the geoid, a long voyage, indicate height variations, even though the ship will always be at sea level. This is because GPS satellites, orbiting about the center of gravity of the Earth, to obtain ones geoidal height, a raw GPS reading must be corrected. Conversely, height determined by spirit leveling from a tidal measurement station, as in land surveying. Modern GPS receivers have a grid implemented inside where they obtain the height over the World Geodetic System ellipsoid from the current position. Then they are able to correct the height above WGS ellipsoid to the height above WGS84 geoid, in that case when the height is not zero on a ship it is due to various other factors such as ocean tides, atmospheric pressure and local sea surface topography. The gravitational field of the earth is neither perfect n If that perfect sphere were then covered in water, instead, the water level would be higher or lower depending on the particular strength of gravity in that location. Spherical harmonics are used to approximate the shape of the geoid. The current best such set of spherical harmonic coefficients is EGM96, the geoid is a particular equipotential surface, and is somewhat involved to compute. The gradient of this also provides a model of the gravitational acceleration
