A graphic map scale, also known as a bar scale, is a visual representation of the relationship between distances on a map and the corresponding distances on the ground. Here's how to use one:
Understanding Graphic Scales
A graphic scale is essentially a line or bar divided into segments, each representing a specific distance. These segments are usually marked with numerical values. According to the provided reference, "a graphic scale is a bar marked off like a ruler with labels outlining the distances the segments represent." Think of it as a pre-made ruler designed for a specific map.
Steps to Use a Graphic Scale
Here's a breakdown of how to use a graphic scale effectively:
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Locate the Graphic Scale: Find the graphic scale on your map. It's typically located in a corner or along one edge of the map.
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Measure the Distance:
- With a Ruler: According to the provided reference "Just as you would with a written or verbal scale to measure distance with this type of scale you would use a ruler". Place the edge of the ruler along the line you want to measure.
- Mark the Distance: If you're measuring a curved path you'll need to carefully measure multiple straight line segments of the path you want to measure.
- Compare to the Graphic Scale: After making your measurements, place the ruler with the marked distance against the graphic scale. Align one end of the marked distance with the zero point of the graphic scale.
- Read the Distance: The point on the graphic scale corresponding with the other end of your measured distance indicates the actual distance on the ground.
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Practical Insights
- Accuracy: The graphic scale's accuracy depends on the map's accuracy and how precisely you make your measurement.
- Proportionality: The graphic scale is designed to be proportional to the map, therefore, it is important to use a straight edge ruler to get the most accurate measurement.
- Map Distortion: Be aware that some maps are distorted to accommodate a globe to a 2-D surface and scales are inaccurate around the edges of these maps.
- Multi-Segment Measurements: It may be necessary to mark multiple segments along a long distance to get the most accurate measurement.
Example
Let's say you measure a distance on your map to be 2.5 cm using a ruler. Then you place your ruler against the map's graphic scale. You see that 2.5 cm on the scale corresponds to 5 kilometers. This means the distance on the ground is 5 kilometers.
Summary
| Step | Action |
|---|---|
| 1 | Locate the graphic scale on your map. |
| 2 | Measure the distance you want to measure using a ruler. |
| 3 | Compare to the graphic scale to determine distance. |
By following these steps, you can effectively use a graphic map scale to determine real-world distances.
