TEXT 29 How maps are made

 

Experts from many fields gather the information that cartographers need. The cartographer then transforms this information into a meaningful visual representation. In general, mapmaking follows these steps: (1) observation and measurement, (2) planning and design, (3) drawing and reproduction, and (4) revision.

Observation and measurement. A variety of experts obtain the information shown on maps. The geodesist provides precise measurements of the earth’s size and shape. The surveyor works out the location and boundaries of places by measuring distances, angles, and elevations. The photogrammetrist obtains measurements from aerial photographs. Some of the other specialists who contribute information include census takers, geographers, geologists, and meteorologists.

The production of new maps based on aerial photographs and other original surveys is called base mapping. Most maps made by base mapping are topographic maps that are large in scale and include much detail. They become the basis for many other maps made by the process of compilation mapping. Compilation mapping involves selecting information from large-scale maps and displaying it on a map at a smaller scale. Cartographers may also compile (collect) information from censuses and other sources for presentation on the finished map.

Planning and design. In planning a map, the cartographer considers the map’s purpose and its likely users. This information helps the cartographer decide which map projection and scale to use and which information to highlight or eliminate. The map’s design helps communicate information effectively. In designing a map, the cartographer selects suitable symbols, writes titles and labels, and chooses lettering. In many cases, a graphic artist helps the cartographer design a map.

Drawing and reproduction. Maps may be drawn in several ways. Cartographers sometimes draw a map directly on paper or plastic drafting film. More commonly, however, they use a technique called scribing. In scribing, the mapmaker uses special tools to cut away the colored surface coating on a sheet of clear plastic. Lines and areas of the clear plastic are thereby exposed. These lines and areas correspond to lines and areas to be printed in ink on the map. Scribing produces maps with sharp, fine lines that would be difficult to achieve by the direct drawing method.

Cartographers today increasingly use computers to draw maps. A device called plotter, which attaches to computer, produces maps by scribing or by drawing with pen and ink. Computers can also use a beam of light from a laser to plot maps by exposing areas of photographic film. In addition, computers can scan base maps, aerial photographs, or actual physical surfaces and then use the data to print a map.

Cartographers often supervise the reproduction of maps so that the correct colors and symbols appear in the proper place on the final map. Most paper maps are printed from printing plates.

Additional steps are needed to produce maps that have a raised surface. These maps include raised relief maps, which have elevated surfaces to represent hills and mountains and tactual maps, which have raised symbols that blind people can read by touch. To make such maps, cartographers first build a three-dimensional model of the map’s raised surface, using plaster or a similar material. Next, the map’s symbols and lettering are printed on a flat plastic sheet. The plastic sheet is then softened by heating, molded to the shape of the three-dimensional model, and hardened.

Revision. Cartographers must revise maps to keep them up to date. For example, changes in the population of cities, the shape of waterways, or the area of forests may require revisions on maps. Aerial photographs are commonly used to survey changes that have occurred since the map was last revised.

 

I. Study the followings words & word combinations:

Representation, surveyor, elevation, boundary, census, scale, compilation, highlight, suitable symbols, eliminate, increasingly, scribing, plotter, beam, expose, tactual maps, plastic sheet.

II. Define the part of speech of the following words from the text:

suitable, producer, cartographer, drawing, compilation, mapping, topographic, meteorologist, population, finished, measuring, aerial.

 

III. Write the following verbs in the Present, Past, Future Perfect Tenses, make up sentences with them:

 

to scribe, to expose, to choose, to eliminate, to highlight, to print, to soften, to produce, to work out, to become.

 

IV. Give your own definitions to the words given below:

 

geodesist, surveyor, base mapping, compilation mapping, scribing, tactual maps.

 

V. Write a short summary of the text “How maps are made” and retell it.