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The cartographic sciences are geodesy, surveying, photogrammetry, remote sensing, geographic information systems (GIS), global positioning systems (GPS) and, of course, mathematics and statistics. In recent years, multimedia and virtual reality became part of the cartographic experience. These are all separate, though somewhat overlapping, disciplines, and they share an intimate relationship with cartography; indeed some have their own cartographic components. A working acquaintance with these fields is an essential part of the education of the modern cartographer.
Geodesy is a very specialized science concerned with determining the shape and size (the ‘figure’) of the earth–not the solid earth, but the geoid, the surface defined by mean sea level–and establishing a framework of points whose locations are known very precisely in terms of latitude and longitude. This is achieved in two ways, by studying the earth’s gravitational field and by conducting very high-accuracy surveying operations. At one time, such work was entirely ground-based, but satellite observations are now routine. Geodesy plays a fundamental role in cartography, for in order to map the earth, it is obviously necessary to know how big and what shape it is and to have reference points of known locations on its surface.
If geodesy is unfamiliar to most people, surveying is quite the opposite, for almost everyone has seen the surveyor at work on city streets with transit, level or distance meter. There are many branches of surveying, including engineering surveys (carried out in connection with construction projects), cadastral surveys (concerned with property boundaries), hydrographic surveys (depicting water bodies) and mine surveys (outlining what is underground). The relation between surveying and cartography is very close indeed, and the end-product of the surveyor’s work is often a map of some sort. One branch of surveying–topographic surveying– has the production of maps as its express aim. Surveying, like cartography, has undergone major changes in recent years, but none so dramatic as those being brought about by Global Positioning Systems (GPS).
Global Positioning Systems (GPS)
A constellation of twenty-four satellites operated by the U.S. Department of Defense comprises GPS. It enables surveyors to determine ground locations very precisely at the click of a button on a hand-held receiver under any weather condition. GPS is revolutionizing the practice of surveying at a very fast pace. Today, a position on the earth’s surface can be determined within fractions of a centimeter. The standard piece of information provided by a GPS receiver is a readout of the calculated latitude and longitude of a given position. These latitude and longitude positions obtained from a GPS can be plotted on a chart or on a map.
Photogrammetry means literally measurement with light and has as its principal aim the production of topographic maps from aerial photographs. An earlier technological change that revolutionized topographic surveying, photogrammetry emerged in the 1930s. Previously topographic maps (large-scale maps in sheet form showing natural and cultural features in the landscape) were produced by traditional ground surveying methods, and while ground surveys are still needed, most of the detail on these maps–the rivers, coastlines, roads, buildings, contours, and so on–is now derived from airphotos. The work is done by the operator of a photogrammetric plotter, a complex piece of machinery that enables one to trace landscape features from a three-dimensional ‘model’ of the earth’s surface created by viewing airphotos stereoscopically. In modern photogrammetry, the movements of the tracing device, or ‘floating mark,’ are translated directly into digital form and the map is plotted automatically.
A more recent discipline, dating from the 1960s, is remote sensing, the process of obtaining information about the earth’s surface using sensors carried in aircraft and satellites. Though the discipline is new, the original form of remote sensing–aerial photography–dates from the nineteenth century, and techniques of airphoto interpretation have long been highly developed. All types of remote sensing involve the measurement of electromagnetic energy reflected from or radiated by the earth’s surface, and photographic cameras (based on visible light) are now accompanied by other sensing devices operating at longer wavelengths. Examples are thermal scanners in the infrared waveband and radar systems in the microwaves. The information obtained may be in image form (like a photograph) or in digital form, and one of the most intriguing applications of remote sensing is the computer processing of digital multispectral data (data obtained simultaneously in more than one waveband) to produce land cover maps of the earth’s surface. Another application of increasing importance is image mapping, the incorporation of a remote sensing image, enhanced by computer processing, into the map itself. Remote sensing, especially sensing from space, is a major source of mappable data, and as such plays a key role in modern cartography.
Geographical Information Systems (GIS)
Another new discipline, perhaps the most exciting of all, GIS is a computer-based system for handling geographical data, that is, data relating to the earth’s surface. The word ‘handling’ conceals a wealth of different operations, however. Some, like data storage and retrieval, are fairly mundane, but others, especially analytical operations like buffering, overlay, network analysis and viewshed modelling, are truly staggering in their potential for solving real-world problems. Maps are integral to a GIS. Data are stored in the computer in the form of ‘layers,’ each in effect a digital map of some component of the landscape (e.g. a streams layer, a roads layer, a soils layer) and analyses are achieved by performing operations on these layers, sometimes one at a time, sometimes on several layers simultaneously. Each stage in an analysis is displayed in map form on a high-resolution computer monitor, and the end-product is very commonly itself a map. GIS has become a billion-dollar business since the early eighties, which is not surprising given the range of proven applications. These include forest management, urban planning, emergency vehicle dispatch, mineral prospecting, retail outlet location, maintenance of public utilities, and waging war, as well as a host of applications with purely scientific ends.
Mathematics and Statistics
Mathematics and statistics are heavily involved in the mapping process, not only because of the geometric aspects of describing locations in space, but also because of clear needs to describe and summarize the characteristics of spatial data. Through creative mathematical approaches, cartographers may find new solutions to solve spatial problems.
Computer systems allow for integrated access to a range of data through the means of stimulation of human senses using digital technology. This includes the integration of images, video and graphics, maps and photographs, text and sound and perhaps in the future smell and taste. This technology has a wide range of applications including education, scientific research, military activities and, of course, entertainment.
Virtual Reality (VR)
A computer system that is able to combine a mixture of real world experiences and computer generated material to allow for simulated real world representation produces a “virtual reality.” VR addresses the construction of artificial worlds with clear spatial dimensions. The movie “Twister” is an excellent example how VR works. These same kind of images can be very useful for the scientist to model or demonstrate an event such as a natural hazard. Cartographers have a major role to play in the identification of VR as a potential research tool.
Cartography and the cartographic sciences are all concerned in some way with data relating to the earth’s surface, whether it be data acquisition, management, analysis or display, and there is a growing trend, driven by a common dependence on computer technology, for the disciplines described here to move even closer together. Reflecting this trend, the term geomatics is used in Canada to denote an integrated multi-disciplinary approach to dealing with earth-related data. In a sense, geomatics is an umbrella term for cartography and the cartographic sciences.