SURVEYING

Surveying
I INTRODUCTION
Surveying, mathematical science used to determine and delineate the form, extent, and position of features on or beneath the surface of the Earth for control purposes—that is, for aligning land and construction boundaries, and for providing checks of construction dimensions. Land boundaries are set or measured for accurate description; the topography of landforms and natural or artificial objects are depicted on maps; and major construction and civil engineering works such as dams, bridges, railways, and roads are controlled by surveying methods. The measurements of a survey are linear or angular, and principles of geometry and trigonometry are usually applied.
II SURVEYING INSTRUMENTS
Horizontal linear measurements are made with calibrated rules or tapes and sometimes electronically by timing the travel of light or radio waves between points. Vertical linear measurements are made with a graduated vertical rod to find differences of elevation and heights above sea level. The so-called engineer's level, a tripod-mounted telescope equipped with a spirit bubble and a cross wire, is used to sight the graduations on the rod. The horizontal or vertical angles are measured by a transit or theodolite, a tripod-mounted telescope with cross wires, the graduated circles of which indicate angles in degrees, minutes, and seconds.
Electronic distance-measuring devices are being perfected and can give extremely accurate results, up to 1 in 6 million or better. Also under development are electronic angle-measuring devices of great precision. Theodolites and transits using glass circles permit greater magnification and can thus be smaller than in the past; these instruments are also more accurate, being capable of measurements to hundredths of a second of arc. An automatic type of engineer's level, employing a pendulum prism or reflecting light from a liquid surface, is also used in place of the spirit-level bubble for differential levelling.
III PLANE SURVEYING
Plane surveys treat any small segment of land or water as a horizontal plane. Such surveys are customarily projected and calculated on a horizontal rectangular grid, oriented north-south and east-west, although the grid can be oriented in an arbitrary, rather than true, north-south direction. From a given starting point, or station, of known or assigned coordinates, the horizontal distance is measured to another point, then to another convenient point, and then to succeeding points, to close on the original point or on any point of known coordinates. A succession of such lines or courses forms a traverse. The horizontal angles between successive courses are measured with a transit or theodolite at each hub, or station. From a known or arbitrarily assigned starting direction, the directions, or bearings, of successive traverse lines can thus be calculated. Plane geometry and plane trigonometry relationships are used to determine the coordinates of traverse stations. The north or south distance of a traverse course is its length multiplied by the cosine of the bearing; the east or west distance of a traverse course is its length multiplied by the sine of the bearing. Coordinates enable the plotting of the hubs to any scale on a grid that can serve as a plot or as control for further details drawn on a map or chart.
Triangulation can be used instead of a traverse, measuring only one baseline, but measuring all the angles in a chain of triangles, to calculated coordinates of successive hubs. The choice of traverse or triangulation is dictated by the type of terrain to be surveyed.
IV GEODETIC SURVEYING
For large areas, surveys must take into account the basic shape of the Earth, the geoid, and are therefore called geodetic surveys. These surveys are based on a spheroidal shape approximating the geoidal or geographic (nearly spherical) shape of the Earth at sea level. They are based on a true north-south meridian as defined by the Earth's rotational axis and on spherical geometry. In the United States, plane-coordinate systems exist for most states, with conversion between plane coordinates and geodetic coordinates made convenient by tabulated relationships. Typically, a road-route survey extending for many kilometres would require geodetic adjustment to avoid accumulation of error resulting from the convergence of meridians.
V LAND SURVEYING
Land surveys are made to establish boundaries of land areas by setting corner markers or monuments, to ascertain coordinates of these corners, and to obtain boundary and area information required for record-deed descriptions and for plotting areas of property. Property surveys are accomplished with a degree of precision depending on the value of the land involved, and permanent visible and recoverable monuments are set at the corners. These markers are desirable for public record and to ensure correct title for the rightful owner of the land. In addition to surveying techniques, land surveyors must also be knowledgeable in property law; registration of practitioners is usually required by law.
VI TOPOGRAPHIC SURVEYING
Topographic surveys are three-dimensional; they employ the techniques of plane surveying and other special techniques to establish both horizontal and vertical control. The relief or configuration of the terrain and the natural or artificial features are located by measurement and depicted on a flat sheet to form a topographic map. Contour lines, connecting points of the same elevation, are used to portray elevations at any one of various intervals measured in metres or feet.
Much topographic mapping is done by means of aerial photogrammetry, which uses stereoscopic pairs of photographs taken by aerial surveys and, more recently, from artificial Earth satellite. Horizontal and vertical ground surveys must appear in the photographs. These photos are then reconstituted into stereo models for drafting true-scale maps. Precise cameras are required; and precision-mapping equipment is used to depict natural and artificial objects in true position and to show true elevations for all points in the mapped area. Elevations on topographic maps are shown chiefly by use of superimposed contour lines, connecting points of equal evaluation, to give a readable picture of the terrain.
VII ENGINEERING AND CONSTRUCTION SURVEYING
Engineering surveys establish control points by traverse, baseline, or other methods to obtain information required for engineering designs and to set out construction from design drawings by use of these control points. Topographic surveys, and the maps produced by them, provide horizontal location information and elevations needed for the design of structures such as buildings, dams, canals, roads, bridges, power lines, and sewers. Using the engineering designs these works are then laid out from the same control points used in the original engineering surveys.
Construction surveying involves the guidance and supervision of engineering surveying dealing with the laying out and building of highways, bridges, dams, tunnels, buildings, and other structures.
VIII CARTOGRAPHIC SURVEYING AND CARTOGRAPHY
Surveys to set control points and to obtain detail for map and chart making are called cartographic surveys. Charts and maps of a small scale (covering large areas) are compilations of larger-scale maps with much detail omitted. Coastal charts depict the shoreline, but show only significant navigation aids along the shorelines and indicate water depths. Air-navigation charts show only significant geographical features, obstructions, air lanes, radio beacons, and guidance features such as railways and roads. See Cartography.
IX HYDROGRAPHIC SURVEYING
The surveying and mapping of sea, river, harbour, or lake bottoms to ensure safe navigation depths are done by hand soundings located by observations to or from control points on shore. Sonar soundings with simultaneous radar-type location of the sounding vessel also permit rapid and exact charting. Farther out from the shore, less accuracy of location results; Loran devices are used for this purpose, and satellite-navigation devices are also used for fairly accurate offshore positioning of vessels furnished with modern equipment.
X MINING SURVEYS
Mining surveying is used to establish surface location and boundaries of mining claims. During mining or tunnelling operations, the mine survey helps to establish the location of the underground workings horizontally and vertically, to lay out shaft connections, and to guide the tunnelling. This is three-dimensional traversing, not essentially different from surface surveying.
Microsoft ® Encarta ® Encyclopedia 2004. © 1993-2003 Microsoft Corporation. All rights reserved.
Cartography
I INTRODUCTION
Cartography, the art and science of map-making. To quote the writer Paul Theroux, “Cartography is the most scientific of the arts and the most artistic of the sciences”.
II THE NATURE OF CARTOGRAPHY
Cartography—or map-making—is both a set of skills and a subject for academic study. The making of maps has traditionally required:

(1) The ability to find and select information from many sources on different aspects of geography, then to synthesize the results into a single, consistent, and accurate set of data. (2) Design skills to create a final map which will correctly portray the intended “message” to readers who vary greatly in their map-reading skills. (3) Manual dexterity to draw the information using symbols, lines, and colours so that “clutter” is minimized and the map is everywhere legible. (4) Graphic design skills to simplify often complex patterns into simple ones.
But maps are not just artistic creations which demonstrate the skills of their creators. They are historical and sociological documents. In Britain, for instance, Ordnance Survey first produced maps from the beginning of the 19th century; these maps are a vital record of the landscape up to the present day, showing long-forgotten industrial works and former railways. They give a clue to land which may be contaminated by past use. A more sinister example is the use of misleading maps as propaganda in Nazi Germany to demonstrate the “threat” to Germans who were being “outnumbered and encircled” by Poles and other Eastern Europeans. In earlier times the use of Mercator's map projection in Britain exaggerated the apparent size of the British dominions in Canada in contrast to the French colonies which were mostly nearer the equator. For this reason, maps and their creators are the subject of much academic study, for they illuminate history.
There is no one “correct” way to make a map. The way it is done depends on the tools available to the cartographer, the purpose of the map, and his or her knowledge base. There are, however, many good “rules of thumb” which can guide the new map-maker.
III DIFFERENT TYPES OF MAP
It is as well to realize that different types of map require different treatments and even different skills to create. The most common subdivision is made between topographic and thematic maps. The first shows the features of the natural and built landscape selected according to some (usually country-wide) specification. This might show the transport networks (roads, railways, canals, footpaths, and airports), hydrographic features (rivers, lakes, and coastal features), settlements (villages, towns, and cities), the shape and altitude of the land, and so on. Thematic maps show, as the name suggests, specific themes (such as the geology of the area), usually on top of the topographic map. But this distinction is not very meaningful, for the topographic map is itself a thematic map. And into which category does land use and land cover fall?
One more substantial distinction is between large- and small-scale maps. The large-scale ones in Europe and some other parts of the world show details of individual houses. Indeed, the most detailed maps are often those showing land and property ownership: those for Sweden have been compiled since the early 17th century. Such maps are usually made at scales between 1:500 and 1:5,000 and little generalization or simplification of the selected information is required. For most practical purposes, the user needs little knowledge of the map projection employed. The more densely populated the area, the larger the scale used.
Small-scale maps, on the other hand, may well be highly generalized. Roads and other features may be moved in order to reduce clutter, provided that the features are still placed in their correct relationship to each other, for example, a road crosses a river over a bridge. In the extreme case (maps at 1:1 million scale and smaller) the result is often a caricature which can be a good illustration yet a very poor source of reliable quantitative information (such as the distance between two places). The map projection chosen may dramatically affect the appearance and value of the map. To complicate matters still further, cartographers in different countries not only produce maps to different specifications—they also call them different things. In the United States, for instance, the official maps at 1:6,500 scale are often regarded as large-scale maps while in the much more intensively mapped Britain these would be regarded as small-scale ones.
Finally, most of “old cartography” has been produced by official mapping bodies which are part of the public service. Commercial cartographers have rarely produced national map series: they have concentrated solely on areas for which there are many customers. In many countries, the commercial cartographers obtain their information (sometimes at no cost but this is becoming more rare) from official ones.
IV THE BIRTH OF THE NEW CARTOGRAPHY
The old cartography flowered after the invention of the printing press. For five centuries cartographers created maps on paper. The methods with which they created the image to be printed evolved from engraving on stone and copper to scribing on plastic and the creation of “colour masks” by sophisticated photographic techniques.
In the last 30 years, and especially since 1990, the situation in cartography has changed radically. This has come about through the introduction of the computer into map-making. The earliest work seems to have been carried out by meteorologists and biologists in Sweden, Britain, and the United States. But the vital work was carried out in a British research group, the Experimental Cartography Unit, in the period from 1968 to 1973, by researchers in Harvard University at about the same time, and thereafter by many others throughout the world.
Several significant changes came out of all the research which have transformed cartography for ever. These are that:
(1) Maps are now commonly made from computer databases. Such maps are one (very important) by-product from the database. The computer is no longer used simply to automate traditional cartographic drawing skills, but has become an engine for checking the quality of data, linking data together, searching to find material of interest, and portraying the results in any way the user desires. (2) Customization of the results is normal. Ordnance Survey's Superplan service, for instance, enables a customer in a shop to select on a computer screen an area of interest of whatever shape. A map is then printed out on paper; what the map contains is a matter for the user to choose, as is the scale within the range of between about 1:100 and 1:5,000. (3) Virtual maps are commonplace. Such maps are produced on a computer screen and may never be printed out in paper form. (4) Data and computer programs to make such maps are increasingly available. As a result, there are now far more maps made than ever before, often by people who are not trained cartographers.
Some of the new maps are fundamentally different to the older “line map” style ones. Geometric distortions in aerial photography and satellite imagery can now be removed by computer. As a consequence, “photomaps” can be made semi-automatically and these are excellent where previous maps are very out-of-date (for example, in many urban areas in the United States) or for certain types of landscapes (for example, estuary or wetland areas).
Many of the national mapping agencies of governments around the world have recognized the effects of technology change and adapted to it. The pioneers have included the mapping agencies in Britain, Sweden, Australia, New Zealand, France, the United States, and Canada.
V GEOGRAPHICAL INFORMATION SYSTEMS
In the period up until about 1985, the various different roles of professionals in topographic mapping were clear and obvious. The geodecist made the detailed instrumental readings and computed results which defined the basic shape of the country. From this information, land surveyors filled in detail on the ground or photogrammetrists provided mapping using aerial photography. Cartographers redrew their efforts into an attractive form which met high standards of graphic elegance and communicated the information effectively and unambiguously. Other collectors of geographic information such as geologists or soil surveyors used these maps as a base on which to collect other details of interest to them.
In the last decade, however, this cosy and stable structure has been rocked by the advent of new technology. Much of the highly skilled work has been replaced by the introduction of the Global Positioning System satellites and new surveying equipment. Data collectors have built into their field computers software which allows them to produce elegance and readability akin to that of their home-based cartographic colleagues. As a result, there has been a significant reduction in the numbers employed in official mapping and tension has arisen between the different groups.
But it is quite wrong to think of this as a declining industry. The commonplace use of computers has resulted in the development of a new set of tools called Geographical Information Systems or GIS. The first of these was built in Canada in 1965 to make an inventory of the state of the fauna and flora across the country. Now there are many tens of thousands of these in use across the world and the numbers are growing at about 20 per cent per year. Indeed, GIS is now claimed to be a multi-billion-dollar business internationally with many major commercial firms involved in creating software and tailoring these to meet the needs of different customers.
The range of tasks that a GIS can be called on to answer is infinite if we consider all the details of what goes on in different human activities, such as marketing a product to a target audience; the storing of details of every utility cable in a nation; recording every land transaction; or modelling global change—GIS are involved in all of these and many more. It is helpful, however, to summarize their capabilities as being able to answer the following generic questions:
(1) What is at ...? (for example, What type of soil exists at latitude X, longitude Y? or What is the population of the Prime Minister's parliamentary constituency?) (2) How do I get from ...to ...? (for example, Give me detailed instructions for driving from Regent Street in London to the Place de la Concorde in Paris) (3) Where is ...true/not true? (for example, Where in the country (or the world) can I find crop type A grown on soil type X?) (4) What has changed since ...? (for example, How much change has there been in rainforest extent in the last 20 years?) (5) What spatial pattern(s) exist(s)? (for example, Where—if anywhere—are there geographical clusters of deaths among children due to cancer of a particular kind?) (6) What if ...? (for example, What if we added another feeder road to the orbital motorway around the capital city? How much would traffic increase and where would the changes occur?)
GIS have one great advantage which has not yet been mentioned: they give us something extra almost for nothing. They are the only tools available to bring together geographical information collected separately by different organizations. Typically these collect such information for their own purposes and the only way it can be related to that of other organizations is through geography. GIS achieve this by “overlaying” one data set on top of another and computing the characteristics of common areas. If there are two data sets (such as soils and crop productivity) for a country, we have one combination. If, however, there are 20 different data sets, there are 190 pairs in combination and over 1 million combinations in total. As a result, data brought together in a GIS can be used for many more purposes than if these are held in separate databases.
GIS have already had an impact on cartography. In the first place, it is a positive development for national mapping organizations like Ordnance Survey, because it ensures that their data are more widely used. But the effects of GIS are much wider. For instance, the traditional map, while it can hold huge amounts of information in a compact space and is most convenient for use in the field, is difficult to use for extracting different kinds of information and combining such information in a meaningful way, tailored to individual needs. On the other hand, the map remains an unrivalled way of depicting variations in geography in a way that many people can readily understand. The combination of a GIS “information sifting and exploring engine” with computer-based cartography is already ensuring a rapid expansion in the role of mapping—even if most of the maps are no longer made by traditional cartographers or in paper form.

Contributed By:
David Rhind
Microsoft ® Encarta ® Encyclopedia 2004. © 1993-2003 Microsoft Corporation. All rights reserved.
Scale (cartography)
Scale (cartography), in cartography, the ratio of the distance between two points on a map and the actual distance between the two points on the Earth's surface. On maps, scale is represented in three ways: as a ratio or fraction, such as 1:50,000 or 1/50,000, which means that 1 unit of measurement on the map equals 50,000 of the same units on the Earth's surface; as a graphic scale, usually a straight line on which distances (most often in kilometres or miles) have been marked off; and as a phrase in words and figures, such as “1 cm represents 100 km” (that is, 1 cm on the map represents 100 km on the Earth's surface). The larger the scale of a map, the closer it approaches the actual size of features on the Earth's surface. Small-scale maps generally show larger portions of the Earth's surface and have less detail than large-scale maps. Because maps are flat and the Earth’s surface is curved, scale may vary within a single map; the scale expressed in the legend is generally accurate near the centre of the map, but less so towards the edges.
Microsoft ® Encarta ® Encyclopedia 2004. © 1993-2003 Microsoft Corporation. All rights reserved.