Y11-12 Geography: Scale and Distance on Maps

Scale and Distance on Maps

Map scale expresses the relationship between a distance shown on a map and the corresponding distance on the ground. Because maps are reduced representations of the real world, scale helps show either a broad area or detailed features.

Ways to Show Scale

• Numerical (ratio) scale: Written as a ratio, such as 1:25,000. One unit on the map represents 25,000 of the same units on the ground. For example, 1 cm represents 25,000 cm, or 0.25 km.
• Verbal scale: States the relationship in words, such as “1 cm on the map represents 500 m on the ground.”
• Linear scale: A marked line on the map represents a stated ground distance. Comparing a measured map distance with the line gives the real-world distance.

Choosing and Understanding Scales

• A large-scale map shows a smaller area in greater detail and has a smaller denominator, such as 1:1,250.
• A small-scale map shows a larger area with less detail and has a larger denominator, such as 1:250,000.
• A 1:25,000 map is useful for a detailed city walk, while a 1:50,000 map covers more ground per centimetre and may suit a longer bike ride.
• The map’s scale should suit its purpose. Too large a scale may require frequent map movement, while too small a scale may omit needed detail.

Measuring Distances

Straight-Line Distance Using a Numerical Scale

1. Place a ruler between the two points, with its zero mark at one point.
2. Make sure the ruler passes through both points, then record the map distance.
3. Multiply that distance by the scale’s denominator. For example, 5 cm on a 1:25,000 map represents 125,000 cm on the ground.
4. Convert the result into a practical unit. Since 100,000 cm equals 1 km, 125,000 cm is 1.25 km.

Using a Linear Scale

1. Measure the distance between the points with a ruler.
2. Compare that measurement with the linear scale to determine the ground distance.
3. Keep the ruler’s zero aligned with the beginning of the scale.

Curved Distance

1. Carefully lay a piece of string or rope along the curved route, starting at the zero mark.
2. Straighten the string and measure its length with a ruler.
3. Apply the map scale and convert the result to suitable units.

For both straight and curved measurements, keeping track of the zero mark is essential for accuracy.

Speakers and Sources

• Speaker: One unnamed narrator or presenter.
• Source: Atomi educational lesson.