Careers in Cartography
How Are Maps Produced ?
This is not an easy question to answer in the space of a few lines, mainly because maps fall into so many different classes, each posing special challenges for the cartographer. Maps can be classified in various ways, by scale, physical form, graphic characteristics and subject matter. In terms of scale (a measure of how much the map is "red need" relative to the real world), maps range from large-scale plans showing individual city blocks to small-scale maps of the whole world. In terms of physical form, maps range from traditional static maps printed on paper and bound in atlases to animated map displays on computer monitors. In terms of graphic characteristics, we have the fundamental distinction between maps produced in black-and-white and maps produced in full color. And finally, in terms of subject matter, we have an almost endless list of map types--topographic maps, navigational maps (subway maps, road maps, nautical charts, aeronautical charts), thematic maps (maps depicting specific themes such as geology, soils and vegetation), statistical maps (maps based on quantitative data, such as population or temperature), and so on.
Whatever type of map is being produced, however, there are certain
key things the cartographer has to do or decide before
he or she ever starts working on a map. A basic decision
has to be made about the study area and the subject matter.
Data have to be obtained and evaluated, and if necessary
processed. A scale has to be chosen, and possibly a map
projection (a mathematical transformation that flattens
out the curved surface of the earth, necessary for maps
of high accuracy or of large areas). Decisions have to
be made about generalization, the process whereby unnecessary
detail (for instance, small settlements or minor sinuosities
in streams) is omitted in order to keep the map clear
and uncluttered. In addition, a host of design choices
is required, such as the shapes, sizes and colors
of symbols, the sizes and styles of lettering, and the overall layout of the map (the positioning of the title, legend, scale bar and so on). Frequently these things are set down in a detailed list of specifications, or are incorporated into a compilation, a preliminary drawn map that serves as a guide for the actual final process.
What happens next varies greatly depending on the type of map being produced. Most cartographers are involved what is called desktop mapping.
Make the assumption a cartographer is producing a black-and-white map of Canada, with rivers, provincial boundaries and major cities, using a general purpose graphics program and a microcomputer. The first task is to input a base map. Today, base maps can be purchased in digital format, or perhaps downloaded from the world wide web. Another way to get a basemap is by using a scanner to convert an existing map, either a published map or a compilation, into digital form.
The scanned image is displayed on the screen as a grey backdrop, and then various graphics tools built into the program are used to trace in black the details to be included in the map. Other tools enable the mapmaker to add patterns, symbols and lettering and progressively builds up the map on the screen. These tools are controlled by a hand-held 'mouse,' which makes for great ease and flexibility in composing the image, including the possibility of making changes at will. Once the map is complete, a laser printer can produce a paper copy almost indistinguishable in quality from the very best maps once produced by hand.
Make the assumption a full-color atlas map of the land use of the Great Lakes Basin is going to produced. This, too, is produced by computer; the colors can be selected by a tool on the computer which colors lines and areas on command. Today's high quality color printers reproduce colors very closely to the ones selected by the cartographer. If the final map needs to be printed or mass produced through offset lithography, the cartographer can provide the printer with a disk showing the color separations. Producing a color map used to be a lengthy painful process!
Mapping with Geographical Information Systems
The final case incorporates GIS analysis into the mapping process. A map is required of the Niagara Peninsula showing areas of tender fruit cultivation, located on sandy soils, between 100 and 120 m in elevation, and within 250 m of major roads.
An extensive digital database of the Peninsula already exists and contains maps (or layers) showing land use, soils and elevations. There is no roads layer, however, so the cartographer prepares his or her own from a published topographic map by using an electronic digitizer. The cartographer then embarks on a sequence of analyzes using the full power of the GIS software. From the land use, soils and elevations layers, three new layers are extracted, one containing tender fruit areas only, another sandy soils only and the third land between 100 and 120 m only. These are then combined by a process known as overlay to produce another new layer that contains only those areas that satisfy all three requirements simultaneously.
The final step is to use overlay once more to determine which of these areas lie within 250 m of major roads, though before doing this, the cartographer has to use a buffering operation to create a band 500 m wide along all the roads in the roads layer. The analysis is then complete, and the finished map appears on the computer screen, to be printed out if desired using some form of color printer or plotter.