In geography, a ratio scale, also known as a fractional scale, is a fundamental way to represent the relationship between distances on a map and the corresponding distances on the Earth's surface. It expresses this relationship as a simple ratio or a fraction.
Understanding Ratio Scale
A ratio scale tells you how much smaller the map is compared to the actual area it represents. The provided reference states:
Ratio or Fractional Scale: the ratio between a distance on a map and the actual distance on the ground – 1:62,500 (or 1/62,500) means that one unit (e.g., an inch) on the map equals 62,500 of the same units on the ground.
This means that the ratio 1:62,500 can be interpreted as:
- Every 1 unit of measurement on the map represents 62,500 of the same units on the ground.
- If you measure 1 centimeter on the map, it corresponds to 62,500 centimeters (or 625 meters) on the ground.
- If you measure 1 inch on the map, it corresponds to 62,500 inches (or approximately 0.986 miles) on the ground.
Key Characteristics
- Unitless: Ratio scales are unitless because the units on both sides of the ratio are the same (e.g., inches:inches, centimeters:centimeters). This makes them universally applicable regardless of the measurement system used.
- Expressed as a Ratio or Fraction: It appears as 1:X (ratio) or 1/X (fraction), where X is the number of ground units represented by one map unit.
- Indicator of Detail: A larger number on the right side of the ratio (e.g., 1:250,000) indicates a smaller scale map covering a larger area with less detail. A smaller number (e.g., 1:10,000) indicates a larger scale map covering a smaller area with more detail.
Examples of Ratio Scales
Here are a few common examples:
- 1:1,000: A very large-scale map, often used for site plans or detailed urban maps. 1 cm on the map equals 10 meters on the ground.
- 1:25,000: A relatively large-scale map, suitable for hiking or detailed local area study. 1 inch on the map equals 25,000 inches on the ground.
- 1:100,000: A medium-scale map, useful for regional planning or road maps. 1 cm on the map equals 1 kilometer on the ground.
- 1:1,000,000: A small-scale map, used for showing large countries or continents. 1 inch on the map equals 1,000,000 inches (or approx. 15.78 miles) on the ground.
Ratio scales are essential for accurately interpreting distances and areas shown on maps in the field of geography.
