A map is a symbolic representation of the arrangement of features in an area. People have used maps for millennia to organize and understand the world. The study of maps and the practice of making them is called cartography.

Some of the oldest known maps are ancient clay tablets made in the ancient civilization of Babylon. Modern maps are tools people use to navigate, to communicate, and to organize information. They are usually two-dimensional images drawn or printed on paper or other materials or displayed on screens. Maps use visual elements like lines, colors, symbols and words to show where things are and to communicate information. Some use shading, tints or patterns to indicate changes in elevation and to show features like mountains and valleys. These techniques help maps create the illusion of height and depth. Some maps, such as globes and terrain models, are three-dimensional representations. Maps used to guide ships or pilot airplanes are often called charts. Today, maps are often viewed digitally using phone and computer screens

Maps come in many forms, sizes and uses. Reading—and creating—maps involves understanding symbols, scale, projection, grids, and lines of latitude and longitude.

Scale

Maps are scaled-down models of places. No matter how big or small a map may be, the distance between one point and another are, relative to the size of the map, intended as accurate representations of actual physical distance. The relationship between actual distance and distance depicted on a map are expressed by visual scales and representative fractions.

The most common type of visual scale is a bar scale, which looks like a ruler. It is a horizontal line marked in uniform increments that represent kilometers, miles or other measurements of distance. For example, a map’s bar scale could indicate that a centimeter on the map represents a kilometer in the real world. Using a ruler, you can easily measure distances in the real world by measuring centimeters on the map. The exact relationship between measurements on a map and measurements in the real world can also be described using representative fractions.

Representative fractions are not specific units like centimeters or miles, but rather describe the relationship between any two units. For instance, a map may have a representative fraction of 1:1,000,000, which means that any unit used on the map represents one million of those same units on Earth. So, one centimeter on the map would represent 1,000,000 centimeters on Earth, or 10 kilometers. This principle applies to all units of measurement. For example, if a map has a representative fraction of 1:50,000, one inch on that map would represent 50,000 inches on Earth, which is just over three-quarters of a mile.

The size of the area depicted, rather than the size of the actual map, determines how a map’s scale might be described. A map that shows a place in a great amount of detail, such as a neighborhood street map, is called a large-scale map because objects on the map appear relatively large. A map of a larger area, such as a whole continent or the entire world, is called a small-scale map because objects on the map appear small.

Today, some of the most commonly used maps are digital maps viewed on screens that allow the viewer to zoom in and out, which changes the map’s scale. For instance, if someone uses their phone to look at a map of the whole world, they would be viewing a small scale map. If they were to then zoom in all the way to their hometown, they would be viewing a large scale map, even though their phone screen remained the same size.

Symbols

In the same way that scale is a representation of actual distance, mapmakers, called cartographers, use many other symbols to represent important information on maps. A small dot might represent an entire city, and yellow lines might represent highways, while blue lines represent borders between countries. The exact symbols, colors, and labels used by cartographers can differ drastically from map to map, so maps usually have a legend or key, which offers not only the bar scale of the map, but also a list of symbols and what they represent on that specific map.

Grids and Lines

Grids are evenly spaced lines running vertically as well as horizontally, creating squares or rectangles across a map. Each column and row of squares is assigned a letter or number. If the columns are labeled with letters and the rows are labeled with numbers, each square can be individually referenced by the letter of the column and number of the row, making it easy to communicate approximate locations. For instance, if a park map includes a list of all the hiking trailheads in the park, a grid would allow them to indicate locations easily, such as “trail begins at D7”.

Grids should not, however, be confused with latitude and longitude. Although latitude and longitude serve similar purposes as a grid, they are part of a standardized system that applies to all maps and globes. Latitude lines run east to west around the globe, parallel to the Equator, an imaginary line that circles the middle of Earth. Longitude lines run north to south, from pole to pole. Latitude and longitude lines are numbered, and the exact point where these lines intersect with each other can be described in numbers, called coordinates, to indicate any location on the planet. Because latitude and longitude are a standardized system that is used across all kinds of maps, those coordinates will always remain the same, regardless of the map.

Because many maps are two-dimensional, it can be difficult to judge the shape of terrain and elevation of any given spot. Topographic lines indicate changes in elevation with many concentric lines, loops drawn inside of each other, usually with notes on the loops to mark elevation. As elevation increases, these concentric lines may indicate a hill or mountain. As elevation decreases, they might indicate a depression in the ground, such as a lakebed or basin. When the elevation changes on a map are subtle, the full “loop” of a topographic line might be too big to depict on the map.

D.O.G.T.A.I.L.S.

With so many symbols, markers and lines, it can be difficult to remember all the elements of a map. One good way to remember is the acronym DOGSTAILS, which stands for Date, Orientation, Grid, Scale, Title, Author, Index, Legend and Sources.

“Date” refers to either the time the map was made or the date relevant to the information on the map. For instance, if a map’s date is 1847, it could indicate that the map was made in 1847. Alternatively, it could indicate that the map depicts data, borders and other information that was true in 1847. Usually, other context clues can help indicate which is true.

“Orientation” refers to the presence of a compass rose or simply an arrow indicating the directions on the map. If only one arrow is used, the arrow usually points north.

“Grid” refers to the lines drawn over a map, whether they be an arbitrary grid or longitude/latitude lines.

“Title” describes what the map depicts, its purpose and contents. For example, a map might be titled something like “Watersheds of Africa” or “Population Map of Canada.”

“Author” indicates the cartographer who made the map. This information offers useful insight into the author’s perspective as they were designing the map.

“Index” is a tool to help users find locations or objects on the map. Typically, the index references grid coordinates.

“Legend” Sometimes called a “key”, this is a list of the symbols, lines and colors that appear on a map and what they mean.

“Sources” refer to where the cartographer obtained the information and data used to create the map. These are vital in assessing the accuracy and objectivity of any given map. These sources might include information from GPS satellites, national survey data or institutional records.

Map Projections

Projecting, or transferring information from the spherical surface of planet Earth onto a flat surface is challenging. A globe, a spherical model of Earth, can more accurately represent the shapes, sizes and locations of all the continents. However, if someone were to cut a globe in half and flatten each of the sides to create a flat map, the result would be warped, torn in places, and unusable. Even if the flattened globe were cleaned up to be a usable two-dimensional map, the size, shape and relative location of the continents would be altered from the original globe.

In order to create a usable two-dimensional map of a spherical planet, some level of distortion is unavoidable. In order to make a map, cartographers decide which parts of the map ought to appear most true-to-life, and which parts can be distorted without affecting the usefulness of the map. The final perspective of the map, including the way in which some parts are distorted or represented more realistically, is called a projection.

There are a huge number of different projections that cartographers employ based on the purpose of their map, but they can be broken down into three basic categories: planar, conical and cylindrical.

In a planar projection, Earth’s surface is projected onto a plane, or flat surface. Imagine touching a globe with a piece of cardboard, mapping that point of contact onto the cardboard, then projecting the rest of the map onto the cardboard around that point. Planar projections are most accurate at their centers, where the plane “touches” the globe. They are often used for maps of either of Earth’s poles.

For conical projections, imagine putting a cone over the globe, putting the tip of the cone right over one of the poles. That is a conical projection. The cone touches the globe along one or two lines of latitude. When the cone is unwrapped and made into a flat map, latitude lines appear curved in circles or semicircles. Lines of longitude are straight and come together at the pole that was directly below the tip of the cone. In conical projection, areas in the midlatitudes—regions that are close to neither the Equator nor the poles—are represented fairly accurately. For this reason, conical projections are often used for maps of the United States, most of which lies in the midlatitudes.

For a cylindrical projection, Earth’s surface is projected onto a tube that is wrapped around the globe. The cylinder “touches” Earth along one line, most often the Equator. When the cylinder is cut open and flattened into a map, the regions near the Equator are the most accurate in size and shape, while regions near the poles are the most distorted. Cylindrical projections are often used for world maps.