For example, a colorful map of the Marquesas Islands with exotic-sounding ports such as Hakapehi on Nuku Hiva might sound appealing to some. Similarly, a detailed map of the many features of Athens or Bangkok might entice others. A map can even be created for the surface of Mars, based on data transmitted to Earth from computer-controlled spacecraft, showing places that most people will never visit.

Maps can be drawn in many different styles, each showing different faces of the same subject and allowing us to visualize the world in a convenient, informative, or stimulating way. The few simple skills and facts described here will help you to use maps effectively. In addition, be aware of these important facts:

• No map is perfect. People make maps from data they collect with certain tools. Even computer-generated maps depend on programmes and machines designed by people. People make mistakes and machines are never totally accurate, no device can record every detail of a landscape. Maps, therefore, can contain errors and inaccuracies. Data or cartographic errors could result in a certain village not being exactly where the map shows or a mountain peak not being exactly as high as it appears on the map.

Cartographers who use traditional tools, such as recording ground data by hand or using high-altitude photography, are limited by how many objects they can record and how small these objects can be. Very small features may not be accurately placed or may not appear at all. Modern tools such as high-resolution satellite photography can record details to a resolution of several meters. Most surface objects of practical importance can be recorded with such imagery and translated into highly accurate maps or photographs, but they are still subject to interpretation and data error. Cartographers sometimes purposely limit the details they present in a map in order to make the map less confusing.

• Maps also become outdated, no longer showing the world accurately. This is because the world is constantly changing both physically and culturally. Modern technology has provided a partial solution-computers have made it possible to renew maps easily without redrawing them. However, appropriate information reflecting changes in the world must still be collected periodically and used to revise the maps' databases.
• Maps are biased. Maps generally do not show every single feature of a chosen geographic area-every tree, house, or road-so the cartographer must decide the projection and scale of the map and the amount of detail to present. The purpose of the map and the cultural background of the cartographer often dictate this process, which is called generalization. Information on the map and how it may be distorted can influence what people think about the world and what they do.

Map Types

An example of a general map is a road map of a country also showing major cities, mountains, rivers, landmarks, etc. The second category is thematic maps, which contain either one or several themes and show in-depth information. Thematic maps can show almost any kind of information that varies from place to place, such as a country's population or income level by state, province, or county, with each division colored differently to indicate the relative level of population or income. The third category of map is charts, which are accurate maps of routes of travel used for ocean and air navigation. They must be updated frequently so that captains and pilots know of current dangers along their route.

Maps are made in many different forms. The first maps made by people were probably lines drawn in sand or small pebbles and sticks arranged on the ground. Modern maps are published for the long-term use of many people. Printed maps are the simplest forms. They show the world as flat-that is, in two dimensions. On a printed map, relief-mountains, valleys, and other terrain-is shown with special symbols to make up for the lack of depth, which is the third dimension. Relief maps are rigid flat maps with actual bumps and depressions added to indicate elevated landforms and low areas. They are usually made of clay or moulded plastic, and the relief is usually exaggerated to give a greater impression of height.

In between the effects created by flat maps and relief maps is the visual experience created by stereograms. These give the effect of viewing actual relief because they stimulate what our eyes see. They use two maps or aerial photographs of the same area but taken from slightly different angles. By looking through a stereoscope, which has two lenses a small distance apart, the eyes synthesize the information to provide a 3-dimensional view. Globes are another way of mapping. They are spherical models of planets such as the Earth or the Moon. They give a more realistic impression of features on a curved surface.

Computer maps are the most versatile. A mapping program can dynamically show many different views of the same subject. It can also allow changes in scale, and incorporate animation, pictures, sound, and Internet links to sources of supplementary information. Computer-generated maps can be updated to present more themes and geographic detail. This is because new information can be entered into their databases over time. Having a powerful digital map is like having dozens of printed thematic maps overlaid on a particular area, each electronically connected to an immense library of information on the main theme and on many related ones.

The way that people use a map depends on the type of map they have and what sort of information they want from it. In the case of simple maps, only one or two types of information may be available and few or no map skills are required to use it. For example, a sketch of a neighbourhood may only show what relationship a particular house has to the street corner or whether it is farther from there to the market or to the school. Even those who cannot read the local language can use such maps. Complex maps, however, can indicate actual distance, the exact location of land features, elevation, vegetation, political divisions, and many other aspects of the world. To interpret such a complex map, some basic map skills are required.

The way the geography of the Earth is taken from the globe and reassembled on a flat surface is called the map's projection. Another way of thinking of projection is that every point on the globe can be projected by a straight line onto a transparent form wrapped around the globe. The shape of the form and how the points are spread onto it determine the type of projection. Some common forms are cylinders, cones, ellipses, and flat planes, giving rise to cylindrical, conic, elliptical, and orthographic projections. 

It is impossible to take information from a curved surface and fit it onto a flat surface with complete accuracy. The only way to keep accuracy is to map on a spherical surface-a globe. Any flat map projection will have to compromise on one of the following: area, distance, or direction. Different projections take different views. 

One often-used projection is called the Mercator projection, named after the Flemish geographer Gerardius Mercator. This is a variation of a cylindrical map. It maintains direction and distance, but area in high latitudes-towards the poles-is compromised. For example, India has a larger area than Greenland, yet on a mercator projection Greenland looks many times larger. 

The Peter's projection, by contrast, represents area as accurately as possible. However, this means that the shape of the land masses becomes distorted.

Scale

Computer maps may have a varying scale that changes according to the "zoom" level of the view. The more zoomed in, or closer you are to the Earth, the larger the depicted scale.

Coordinate Position

Latitude is measured from zero at the equator to 90 degrees north and south at the poles. Longitude is measured from zero to 180 degrees west and east. The reference lines for counting are the equator, for latitude, and a line drawn through Greenwich in England, the prime meridian, for longitude. These are the zero lines. A degree of latitude is equivalent to about 112 kilometers (70 miles). Longitudinal lines converge toward the poles, meaning that degrees of longitude vary according to the position on the Earth. At the equator, one degree of longitude is the same length as one degree of latitude, and at the north and south poles, the distance between degrees of longitude is zero.

Degrees are divided into 60 minutes, and each minute is divided into 60 seconds. For example, the Eiffel Tower in Paris has the following coordinates: latitude 48° 51' 32" north and 2° 17' 35" east. Sometimes, coordinates are expressed in decimal minutes instead of minutes and seconds, so the coordinates of the Eiffel Tower can also be written as 48° 51.5333 north latitude and 2° 17.5833 east longitude.

Most official maps indicate latitude and longitude, so viewers know exactly what part of the Earth the map represents.

Some maps have other special-purpose coordinate systems, such as the State Plane Coordinate System used on maps in the United States or the Universal Trans-Mercator (UTM) system used on many military maps.

Legend

Direction: Which Way Is Up?

Modern maps usually adopt the convention that the top of the map corresponds to North, the bottom to South, the left edge to West, and the right edge to East. Direction can also be determined from coordinates, if they are shown. Using the maps in Encarta World Atlas is like holding a globe in your hands-any view of the Earth can be examined. All views are oriented with North as up except when the map is centered on the North Pole or South Pole.

The poles representing the rotational axis of the Earth do not correspond to the magnetic poles-the direction in which a compass points. This is because the magnetic poles constantly change position or wander. The north-pointing arrow on many accurate maps is divided into two parts, one indicating polar and one indicating magnetic north. The angular difference between these is known as the map's magnetic declination. 

For example, according to a 1987 map of Moscow, the compass points to magnetic north at 7° 46' to the right of true polar north, so the magnetic

The Ups and Downs of Maps: Elevation

Modern maps show mountains in shaded relief, called hill shading. Traditional topographic maps use concentric lines, called contour or hypsographic lines, to indicate elevation. Each line is assigned a height above sea level. These lines link all places of the same elevation and are usually marked at a regular interval. Having a lot of lines together indicates a rapid change in elevation; longer spaces between indicate flatter land. Corresponding lines indicating ocean depth are called hydrographic lines.

Instead of concentric lines, color maps often use a standardized color scale to indicate elevation: sea level is blue; low elevations are shades of green; higher elevations range from tan to brown; and the highest peaks are shown in white, suggesting snow. Deeper shades of blue correspond to deeper parts of lakes or oceans.

Learning to read maps is easy and intuitive. A person can use the map skills discussed in this article to solve navigation problems, plan future activities, or discover more about the world.