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Cartography | Article View | |
| I. | |
Introduction |
Cartography, the art and science of map-making. To quote the travel-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 traditionally requires:
Maps appear in many forms and media from antique collector’s prints, through modern digital topographic maps, navigation charts, and reference atlases, to images created “on demand” on the World Wide Web. 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. 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 Eastern Europeans. In current times mapping techniques extend beyond the simple recording of information to applications in many scientific, medical, and government situations to assist planning, management, and decision-making. For this reason, maps and their creators are the subject of much academic study, for they illuminate history and provide models for future improvements.
There is no one “correct” way to make a map. The way it is done depends on the facilities 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 |
Different types of map require different treatments and even different skills to create them. 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. The shape and altitude of the land is shown along with man-made features such as the transport networks (roads, railways, canals, footpaths, and airports), hydrographic features (rivers, lakes, and coastal features), settlements (villages, towns, and cities), and so on. Feature names are a particularly important aspect of map detail. Thematic maps show, as the name suggests, specific themes (such as the geology or population density of an area), usually overlaid on a topographic base. 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?
Scale also creates an important categorization for maps. As scale becomes smaller there is less room to show features of the world. Feature simplification (known as cartographic generalization) is the solution. Large-scale maps require minimal generalization; the large-scale ones of 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. 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.
With the advent of computer-stored map data, the dream of cartographers and users is the capability to obtain “scale free” data. In theory, one complete data-set could produce every map ever needed. The cartographer would simply select from the data-set the categories of feature needed for the map—perhaps forestry or flood-hazard areas. The software would then extract the data and produce the required map at the required scale. If the required scale were large, for example a few miles of river valley, the data would be displayed with virtually no generalization; at the other extreme, a map of world forestry areas to fit an A4 page would be very greatly generalized. To date this “perfect solution” is still unavailable. Data-sets are still linked to the scale at which they are generated, although some “zooming” is available.
Much “old topographic cartography” was produced by official mapping bodies which were part of the public service. Commercial cartographers have rarely produced national map series: they have concentrated solely on areas for which there is an identifiable market. Today, in an era of fiscal prominence, data and the information derived from it is highly valued. For obvious commercial reasons, legal and technical charges are made for access to and use of geographical data. Copyright is one contentious aspect. Often, use of maps and images is restricted through a number of structured licensing agreements imposed as the map is compiled from different source companies. To provide an alternative to such restrictions, and encourage innovative use of map data, organizations have evolved, providing more open methods such as Creative Commons licensing.
| IV. | |
Modern Cartography |
The old cartography flowered after the invention of the printing press. For 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 recent decades, and especially since 1990, the situation 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 cartographic 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. Today virtually all maps, for whatever output medium, are compiled on a computer from data collected and stored in digital format.
Several significant changes came out of all the research, which have transformed cartography for ever. These are that:
The definition of maps has expanded to include new types in addition to the conventional “line map” style. Geometric correction to aerial photography and satellite imagery is now mathematically completed by computer; high-resolution aerial photography world coverage is increasingly obtainable; digital elevation model data is available at global and local resolutions. As a consequence, “photomaps”, “hybrids”, and pseudo 3-D images are now called “maps”. These provide excellent coverage where no maps exist, current maps are not up to date, or for types of landscapes where access is awkward (for example, wetlands). MS Virtual Earth and Google Earth provide free access to imagery of the world for viewing in both 2- and pseudo 3-dimensions while in-vehicle navigation systems now use oblique map views.
Many of the national mapping agencies of governments around the world recognized the effects of technology change and adapted to it. The pioneers including the mapping agencies in Britain, Sweden, Australia, New Zealand, France, the United States, and Canada now run fully operational digital systems and positively promote development of creative new map applications.
| V. | |
Geographical Information Science |
In the period up until about 1985, the various different roles of professionals in topographic mapping were clear and obvious. The geodesist made the detailed instrumental readings and computed results which defined the basic shape of the country (see Geodesy). From this information, land surveyors filled in detail on the ground or photogrammetrists provided mapping using aerial photography. Cartographers compiled 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. They also formed the outline base map for statistical thematic mapping.
This cosy and stable structure was rocked by the advent of new technology. Much highly skilled work has been replaced by the introduction of the Global Positioning System (GPS) satellites, new surveying equipment, and technology in general. The boundaries between the separate roles became blurred as field workers accessed their databases remotely; software mapping functions improved and the non-specialist became the “new mapmaker”.
But it is quite wrong to think of this as a declining industry, in fact totally the opposite is true. The development of the set of tools called a Geographical Information System (GIS) has transformed the geographic information-based professions. The separate roles of geodesist, surveyor, cartographer, geographer, and all users have come together to form a “new” discipline, Geographic Information Science (sometimes GeoInformatics or Geomatics). The original GIS, built in Canada in 1965, consisted of an inventory of the state of the fauna and flora across the country. Nowadays, systems are in use around the world, linking and holding data and metadata on an extensive range of subjects. Innovative exploitation is expanding daily, enhanced by worldwide communication facilities.
The range of tasks that the Geographic Information Scientist may 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; storing details of every utility cable in a nation; recording every land transaction; or modelling global change—GIS tools are involved in all of these and many more. It is helpful, however, to summarize the capabilities as being able to answer the following generic questions:
Modern GIS has a great advantage. The system can bring together geographical information collected separately by different organizations. Typically these collect information for their own purposes and the only relation to other organizations is through geography, that is, location. Using this location information (latitude and longitude or grid coordinates), the GIS “overlays” one data set on top of another and computes 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. Much effort is expended in developing compatible or even better a single data specification standard for use in recording, transferring, and processing spatial data. Such are the characteristics of spatial data including definition of point, line, and area relationships that it requires an extensive system definition.
Geographic Information Science has 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 and encourages wide use of the organization’s data. But the effects 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 as an analytical tool. A digital database on the other hand can be queried and different kinds of information extracted, combined in a meaningful way, and its display tailored to individual needs. Then again, the map remains an unrivalled way of depicting variations in geography such that many people can readily understand. The extension of the GIS toolbox, that is, the “information sifting and exploring engine”, to include better cartographic capability, is ensuring a revival and expansion in the use of mapping—new users are exploring and experiencing the skills and knowledge of traditional cartography and even the paper map is still in demand.