Maps use scales to represent the relationship between distances on the map and the corresponding distances on the ground. There are primarily three common types of scales you'll find on maps, as highlighted in geographic resources: written or verbal scale, a graphic scale, or a fractional scale.
These scales are crucial for accurately interpreting distances and understanding the true size of the areas depicted on a map.
Understanding Map Scales
Map scales are essential tools for anyone using a map for navigation, planning, or analysis. They allow you to translate measurements from the flat surface of the map into real-world distances. Without a scale, a map would simply be a diagram of relative positions, but not an accurate representation of the earth's surface.
Let's delve into the three main types of scales:
1. Written or Verbal Scale
This is the most straightforward type of scale to understand as it's expressed in words. It directly states the relationship between a unit of distance on the map and a unit of distance on the ground.
- How it works: It uses phrases like "one inch represents ten miles" or "1 centimeter equals 5 kilometers."
- Example: According to the reference, a written or verbal scale uses words to describe the relationship between the map and the landscape it depicts, such as one inch represents one mile.
- Pros: Easy to grasp quickly.
- Cons: Can become inaccurate if the map is resized (copied, scanned, etc.), as the text scale doesn't change even if the map dimensions do.
2. Graphic Scale (Bar Scale)
A graphic scale is a visual representation of distance. It appears as a line or bar divided into segments, with each segment representing a specific distance on the ground.
- How it works: You measure a distance on the map, then compare it directly to the segments on the graphic scale to find the real-world distance.
- Appearance: Usually a solid bar marked with distances like 0, 10, 20, 30 miles or kilometers.
- Pros: Remains accurate even if the map is resized, as the bar scale changes proportionally with the map.
- Cons: Requires measuring the distance on the map and then comparing it to the bar.
3. Fractional Scale (Ratio or Representative Fraction - RF)
A fractional scale expresses the scale as a ratio or fraction, such as 1:100,000 or 1/100,000. This means that one unit of distance on the map represents 100,000 of the same units of distance on the ground.
- How it works: Both the map unit and the ground unit are the same (e.g., 1 inch on the map represents 100,000 inches on the ground, or 1 centimeter on the map represents 100,000 centimeters on the ground). You need to convert these units if you want to understand the distance in miles or kilometers.
- Example: A scale of 1:24,000 means 1 unit on the map is 24,000 units on the ground. If the unit is inches, then 1 inch on the map equals 24,000 inches (which is 2,000 feet) on the ground.
- Pros: Universal – the ratio works regardless of the unit of measurement used (inches, centimeters, etc.).
- Cons: Requires calculation to convert the ground unit into more commonly used distances like miles or kilometers.
Comparing the Scales
Here's a quick comparison of the three types:
| Scale Type | Description in Words | Appearance | How it Works | Accuracy on Resizing |
|---|---|---|---|---|
| Written/Verbal | States the relationship (e.g., "1 inch = 1 mile") | Text phrase | Read the statement directly. | Inaccurate |
| Graphic/Bar | Visual representation of distance. | A bar with marked segments. | Measure map distance and compare to the bar. | Accurate |
| Fractional/Ratio | Expressed as a fraction or ratio (e.g., 1:50,000) | Numbers in a ratio or fraction (e.g., 1:50000) | One unit on map equals that many same units on the ground (requires conversion). | Accurate |
Choosing the right scale type depends on the map's intended use and medium. For printed maps that might be copied, graphic and fractional scales are generally preferred due to their accuracy upon resizing. Written scales are often used for simplicity on digital maps or when resizing isn't a concern.
Understanding these scale types is fundamental to using maps effectively, whether for navigation, planning, or simply appreciating the vastness of the world.
