Using an atlas

• Atlases show a variety of different maps at different scales.
• Atlases can be used to show physical, political or thematic information.
• Although atlases are useful, they do have certain limitations.

An atlas is a book that shows a variety of different maps at different scales. They usually contain maps of the world, continents and countries. The maps they include can be physical, political or thematic:

• Physical maps show the natural features of the land such as mountains, rivers and lakes.
• Political maps show national boundaries and major urban areas such as towns and cities.
• Thematic maps show information on a particular theme, such as rainfall, levels of wealth or the location of biomes. These may be presented as choropleth maps.

In addition to this, atlases often include other relevant information such as tables of statistics for countries, such as life expectancy or measures of wealth.

Although atlases are a valuable resource, they do have limitations, especially when compared to Geographic Information Systems (GIS) such as those found online. It would be impossible to include the same amount of detail in an atlas as we can online. We can't zoom in to an atlas to view a place at street level, for example. Nor can we add or remove layers such as aerial photography. As with all maps, atlases become outdated very quickly but they can't be as easily updated as online versions.

Another limitation of an atlas is that as maps are flat, and the world is spherical, all maps are distorted. The map projection we normally use is called the Mercator projection. This has some advantages over other projections but it has been criticised for influencing people's worldview as it makes landmasses far from the equator seem larger than they really are. For example, on a Mercator projection, Greenland appears to be the same size as the continent of Africa, when in reality Africa is 14 times larger.

Another projection sometimes used is known as The Peters World Map or the Gall-Peters projection. In this projection, landmasses are the correct size relative to each other. However, these are still distorted, with areas stretched near the Equator and squashed at the poles.

Atlases always contain a table of contents and an index which makes it easier to find a specific map or place.

The table of contents is found at the front of the atlas and lists the main sections included in the atlas in order of page number. These sections are usually divided up by continent but there may be other sections such as satellite imagery or tables of statistics.

The index is found at the back of the atlas and lists towns, cities, countries and continents in alphabetical order. Next to each place name is a list of all the pages in the atlas this location can be found. Often a town or city will appear on multiple maps at different scales and covering different topics.

Next to each location in an atlas index, you will usually also find its latitude and longitude coordinates.

World maps are divided into a grid which shows latitude and longitude. Latitude and longitude are measurements of an angular distance measured in degrees. They are shown using the symbol °. As in maths, each degree is then divided into 60 minutes shown using the ' symbol.

The city of Liverpool, for example, is 53 degrees and 24 minutes north of the Equator (0° latitude) written as 53°24'N, and 2 degrees and 58 minutes west of the Prime Meridian (0° longitude) written as 2°58'W. Liverpool's location can therefore be written as 53°24'N, 2°58'W.

Some of the lines of latitude on a world map have names. There are five major lines of latitude:

• the Arctic Circle (66.5°N)
• the Tropic of Cancer (23.5°N)
• the Equator (0°N)
• the Tropic of Capricorn (23.5°S)
• the Antarctic circle (66.5°S)

There are only two named lines of longitude. These are the Prime or Greenwich Meridian which is at 0° and the International Date Line which is roughly 180°. When you cross the International Date Line the day and date changes, either forward or backward one day, depending on which way you travel.

For example, if a ship sails east across the Pacific Ocean and crosses the International Date Line on May 5th, the date will jump backward to May 4th. If however the ship was sailing west on May 5th and crossed the line, the date would jump forward to May 6th.