adminMaps are the basic tools of geography. They enable us to depict spatial phenomenon on paper. There are conventions used in cartography which allow a map to be read efficiently and quickly.
A good map will have a legend or key which will show the user what different symbols mean. For instance, a square with a flag on top usually represents a school and roads are represented by a variety of widths and combinations of lines. The symbols differ in different places. The symbol for a secondary highway on a USGS Topographic map is equivalent to a railroad in Switzerland. Make sure to read the legend and you’ll understand the symbols.
Every map is a representation of a larger portion of the earth. It is drawn to scale which is the relationship between the map and the actual distance on earth represented on the map.
Without a north arrow, it is difficult to determine the orientation of a map. With a north arrow (pointing in the correct direction), a user can determine direction. Some maps, such as topographic maps, will point to “true north” (the North Pole) and to magnetic north (where your compass points, to northern Canada). A neat line is the border of a map. It helps to define the edge of the map area and obviously keeps things looking “neat.”
Since the map is a flat representation of the curved surface of the earth, all maps are inherently inaccurate. There are a variety of projections which have been formulated for different uses.
A map’s title provides important clues about the cartographer’s intentions and goals. You can hope to expect entirely different information on a map titled “Unemployment in Harare” versus “Topography of Matopos.”
Map colours
Colour appears so often on maps that we often take it for granted that mountains are brown and rivers are blue. Just as there are many types of colour maps, there are also many different colour schemes used by cartographers. The map user should look to the legend for an explanation of colours on a map.
Cartographers utilise colour on a map to represent certain features. Colour use is often consistent across different types of maps by different cartographers or publishers. Map colours are always consistent on a single map.
Many colours used on maps have a relationship to the object or feature on the ground. For example, blue is almost always the colour chosen for fresh water or ocean (but blue may not just represent water).
Political maps, which show more human created features (especially boundaries), usually use more map colours than physical maps.
Political maps will often use four or more colours to represent different countries or internal divisions of countries (such as states). Political maps will also use such colours as blue for water and black and/or red for cities, roads, and railways. Political maps will also often use black to show boundaries, differing the type of dashes and/or dots used in the line to represent the type of boundary — international, state, or county or other political subdivision.
Physical maps commonly use colour most dramatically to show changes in elevation. A palette of greens is often used to display common elevations. Dark green usually represents low-lying land with lighter shades of green used for higher elevations. In the higher elevations, physical maps will often use a palette of light brown to dark brown to show higher elevations. Such maps will commonly use reds or white or purples to represent the highest elevations on the map.
With such a map that uses shades of greens, browns, and the like, it is very important to remember that the colour does not represent the ground cover. For example, just because the Mojave Desert is shown in green due to the low elevation, it doesn’t mean that the desert is lush with green crops. Likewise, the peaks of mountains shown in white does not indicate that the mountains are capped in ice and snow all year long.
On physical maps, blues are used for water, with darker blues used for the deepest water and lighter blues used for more shallow water. For elevations below sea level, a green-grey or red or blue-grey or some other colour is used.
Road maps and other general use maps
These are often a jumble of colour. They use map colours in a variety of ways…
Blue — lakes, rivers, streams, oceans, reservoirs, highways, local borders
Red — major highways, roads, urban areas, airports, special interest sites, military sites, place names, buildings, borders
Yellow — built-up or urban areas
Green — parks, golf courses, reservations, forest, orchards, highways
Brown — deserts, historical sites, national parks, military reservations or bases, contour (elevation) lines
Black — roads, railroads, highways, bridges, place names, buildings, borders
Purple — highways, (also used on USGS topographic maps to represent features added to the map since the original survey)
As you can see, different maps can use colours in a variety of ways. It is important to look at the map key or map legend for the map you are using to become familiar with the colour scheme, lest you decide to turn right at an aqueduct.
Map Scale — Measuring Distance on a Map
A map represents a portion of the earth’s surface. Since an accurate map represents the land, each map has a “scale” which indicates the relationship between a certain distance on the map and the distance on the ground. The map scale is usually located in the legend box of a map, which explains the symbols and provides other important information about the map. A map scale can be printed in a variety of ways.
A ratio or representative fraction (RF) indicates how many units on the earth’s surface is equal to one unit on the map. It can be expressed as 1/100000 or 1:100 000. In this example, one centimetre on the map equals 100 000 centimetres (1 kilometre) on the earth.). Another common scale is 1:1 000 000 (1 cm to 10 km).
A word statement gives a written description of map distance, such as “One centimetre equals one kilometre” or “One centimetre equals 10 kilometres.” Obviously, the first map would show much more detail than the second because one centimetre on the first map covers a much smaller area then on the second map. Some methods of indicating map distance would be ineffective if the map is reproduced by a method such as photocopying and the size of the map is modified. If this occurs, and one attempts to measure an inch on the modified map, it’s not the same as an inch on the original map.
A graphic scale does solve this problem because it is simply a line marked with distance on the ground which the map user can use along with a ruler to determine scale on the map. As long as the size of the graphic scale is changed along with the map, it will be accurate.
Maps are often known as large scale or small scale. A large scale map refers to one which shows greater detail because the representative fraction is a larger fraction than a small scale map which would have an RF of 1/250000 to 1/7500000. Large scale maps will have a RF of 1:50 000 or greater (i.e. 1:10 000). Those between 1:50 000 to 1:250 000 are maps with an intermediate scale. Maps of the world which fit on two textbook pages are very small scale, about 1 to 100 million — google.about.com
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