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.