A verbal scale is a statement that connects distance on a map to distance on Earth. A vocal scale would say, for example, "one centimeter equals one kilometer" or "one inch equals eight miles." There are no units for **the representative fraction**. Since most people can't make out scales any smaller than a quarter, many scales only go up to eight miles (13 km).

A metric scale uses millimeters for its unit of measurement and tells us that 1 mm equals 0.001 meter. This is useful because even though meters and centimeters are similar in size, having a scale that matches the size of the marker helps to avoid confusion when comparing distances across maps. The term "metric system" means using meters for **all measurements**, but this isn't necessary. You can use kilometers instead if you want to.

An imperial (English) scale uses inches for its unit of measurement and tells us that 1 inch equals 2.5 centimeters. This is different from **the metric scale** because it takes advantage of size differences between meters and centimeters by using a factor of two. For example, one inch on an imperial scale is equal to five centimeters on a metric scale. Because of the way it is constructed, this scale cannot be used to compare distances across maps.

A nautical (US) scale uses fathoms for its unit of measurement and tells us that 1 fathom equals **20 feet**.

A verbal scale describes the link between a map distance and a ground distance in words. Typically, it is something along the lines of "one inch equals 16 miles." These scales are used when there is not enough space on the map to display all the details or when there is not a uniform size reference for all areas of the map.

A numerical scale shows the relationship between map distances and ground distances by using numbers. There are three types of numerical scales: linear, logarithmic, and decimal. The linear scale is the most common type of scale you will find on **modern maps**. It works by dividing a region into equal intervals, usually miles or kilometers. Each division represents one unit on the map. For example, if one end of the line has **60 degrees** North latitude and the other end has 90 degrees North, then that means that north is closer to the viewer at **each point** along the line.

The logarithmic scale groups points together according to their relative distances from a central point. It is used less commonly than the linear scale because there are more divisions per unit distance on a linear scale than on a logarithmic scale.

A representative fraction, or RF, depicts the connection between one unit on the map and one unit on the ground. For example, if the RF for a given scale is 0.5, then going from the top of a map to the bottom, will move you 0.5 inches; traveling 16 miles would be equivalent to going around three times.

When printed maps first became available, they usually did not include **any information** about how far each scale value corresponded to **a ground distance**. As a result, people used to estimate how far something was based on the size of the print. For example, if there was a road at the bottom of the map that looked like it was probably 10 miles long, then it could be estimated that the smallest feature that could be seen from space was about 100 feet wide (10 miles divided by **0.5 inch** per RF).

As cartographers improved their maps by including more detail than just roads, these new maps required someone to estimate what scale values meant what distances on the ground. This process is called "marking off" distances on the map. The first person to do this was apparently Thomas Jefferys, who published a book in 1770 entitled A Geographical Grammar.

Scale is defined as the ratio of the distance on a map to **the comparable distance** on the surface represented by the map. This illustration shows that 1 inch on the map corresponds to 16 miles on the Earth's surface. This is the simplest scale to grasp because it use commonly used units. Actual scales will vary, but this is about **the most common type** found in U.S. maps.

It is important to understand that a map's scale can be either geographic or nongraphic. Geographic scales refer to distances on the surface of the earth and are usually shown in miles or kilometers. Nongraphic scales include measurements such as millimeters for medical charts and photographs, and centimeters for body parts.

In general, smaller scales are used for **detail maps** and larger scales for broad-brush topographic maps. Detailed maps show cities, towns, highways, bridges, etc. Broad-brush topographic maps show continental relief including landforms and boundaries between water bodies and terrestrial features.

Maps are created from government agencies, private companies, and individual artists. The National Map Gallery at the University of Texas at Austin has **many examples** of national and state maps available for viewing.

Under this program, students work with **federal agencies** and other organizations to create high-quality digital maps using modern technology.

If the scale is a spoken statement (for example, "1 inch = 1 mile"), just measure the distance with a ruler. For example, if the scale states 1 inch Equals 1 mile, then the physical distance on the ground is that number in miles for every inch between two spots on the map. If there are no inches or feet stated on the map, use this formula: Mileage = Distance / 1350. The 1350 comes from dividing the number of miles into the vehicle's total number of miles per gallon. For example, if a car gets 20 miles to the gallon, and the mileage shown on the map is 50 miles, then you can calculate that the car has an extra 30 miles worth of fuel left after driving it all the way across the country.

Mileage markers also show up on some maps when you get close to certain points of interest. For example, if you're near your destination and want to know how much farther you have to go, look for signs that say "mile marker xxx" or something similar. These markers can help you avoid getting lost en route.

Finally, some maps will indicate low-fuel status on the mileage markers themselves. This can be done by coloring **the marker red** instead of black and white, for example. When you reach a marker that reflects poor fuel economy, stop immediately so you don't waste **any more gas** than necessary.