How to Measure a Straight Line Distance Using a Topo Map
Lay a piece of paper down on the map and mark it., Hold your measurement up to the bar scale., Interpret the largest portion of distance from the primary scale., Read the extension scale for the smaller numbers.
Step-by-Step Guide
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Step 1: Lay a piece of paper down on the map and mark it.
Place a straight edge of a piece of paper onto your map.
Line up the edge with both the first (“point A”) and second (“point B”) points you want to measure the distance between, then make a tick mark on the paper where each point is.Make sure your piece of paper is long enough to make your two tick marks.
Note that this method of measuring using a bar scale works better for shorter line distances.
Hold the edge of the paper still on the map and make sure you mark as accurately as possible where the paper lines up to your two points. -
Step 2: Hold your measurement up to the bar scale.
Locate the bar scale on your topographic map, which is typically found in the lower left.
Place your piece of paper with the two tick marks against the bar scale to begin to read the distance indicated.
Use this method if you have a short distance between your tick marks that easily fits within the given bar scale.
Note first the ratio that is represented by the bar scale.
This indicates that one unit of measurement on the map equals a certain number of units on the ground.
For instance, a common topo map might have a 1:100,000 scale, where 1 centimeter equals 1 kilometer; a 1:63,360 scale, where 1 inch equals 1 mile; or a 1:24,000 scale, where 1 inch equals
0.38 mile and 1 centimeter equals
0.24 mile.Note that on the bar scale there is typically a primary scale, which shows whole units increasing from the 0 point, left to right.
There is also an extension scale, which shows fractions of a unit increasing from the 0 point, right to left., Align the tick mark on the right side of your paper edge with a whole number in the primary scale of the bar scale.
The left tick mark should fall somewhere within the extension scale.
Where you line up your right tick mark on the primary scale will depend on what it takes to fit your left tick mark onto the extension scale.
Keep the right tick mark on a whole number.
The whole number you have your right tick mark on indicates that your ground distance is at least as many meters/kilometers/miles as the scale indicates for that number.
You will find the rest of the distance more precisely with the extension scale. , Determine the rest of your measurement in smaller increments using the extension scale of the bar scale.
Where your tick mark lands will indicate what tenth of a whole unit will be added to your total measurement.
The segments on the extension scale are typically small rectangles, alternately shaded and unshaded for easy reading.
You may also guesstimate at even smaller increments by visually dividing each rectangle into tenths and seeing where the tick mark falls within the rectangle.
For example, on a bar scale that shows 1,000 meters for every inch:
If you align your right tick mark on the 3 mark, you have at least 3,000 meters in your measurement.
If your left tick mark falls on the rectangle in the extension scale that indicates 900 meters, you have an additional 900 meters in your measurement.
If your left tick mark falls right in the middle of the 900 meter rectangle, you could visually divide the rectangle to a tenth of the meter, so you have another 50 meters.
Your total measurement would then be 3,950 meters. -
Step 3: Interpret the largest portion of distance from the primary scale.
-
Step 4: Read the extension scale for the smaller numbers.
Detailed Guide
Place a straight edge of a piece of paper onto your map.
Line up the edge with both the first (“point A”) and second (“point B”) points you want to measure the distance between, then make a tick mark on the paper where each point is.Make sure your piece of paper is long enough to make your two tick marks.
Note that this method of measuring using a bar scale works better for shorter line distances.
Hold the edge of the paper still on the map and make sure you mark as accurately as possible where the paper lines up to your two points.
Locate the bar scale on your topographic map, which is typically found in the lower left.
Place your piece of paper with the two tick marks against the bar scale to begin to read the distance indicated.
Use this method if you have a short distance between your tick marks that easily fits within the given bar scale.
Note first the ratio that is represented by the bar scale.
This indicates that one unit of measurement on the map equals a certain number of units on the ground.
For instance, a common topo map might have a 1:100,000 scale, where 1 centimeter equals 1 kilometer; a 1:63,360 scale, where 1 inch equals 1 mile; or a 1:24,000 scale, where 1 inch equals
0.38 mile and 1 centimeter equals
0.24 mile.Note that on the bar scale there is typically a primary scale, which shows whole units increasing from the 0 point, left to right.
There is also an extension scale, which shows fractions of a unit increasing from the 0 point, right to left., Align the tick mark on the right side of your paper edge with a whole number in the primary scale of the bar scale.
The left tick mark should fall somewhere within the extension scale.
Where you line up your right tick mark on the primary scale will depend on what it takes to fit your left tick mark onto the extension scale.
Keep the right tick mark on a whole number.
The whole number you have your right tick mark on indicates that your ground distance is at least as many meters/kilometers/miles as the scale indicates for that number.
You will find the rest of the distance more precisely with the extension scale. , Determine the rest of your measurement in smaller increments using the extension scale of the bar scale.
Where your tick mark lands will indicate what tenth of a whole unit will be added to your total measurement.
The segments on the extension scale are typically small rectangles, alternately shaded and unshaded for easy reading.
You may also guesstimate at even smaller increments by visually dividing each rectangle into tenths and seeing where the tick mark falls within the rectangle.
For example, on a bar scale that shows 1,000 meters for every inch:
If you align your right tick mark on the 3 mark, you have at least 3,000 meters in your measurement.
If your left tick mark falls on the rectangle in the extension scale that indicates 900 meters, you have an additional 900 meters in your measurement.
If your left tick mark falls right in the middle of the 900 meter rectangle, you could visually divide the rectangle to a tenth of the meter, so you have another 50 meters.
Your total measurement would then be 3,950 meters.
About the Author
Jean Clark
Creates helpful guides on DIY projects to inspire and educate readers.
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