Make sure your piece of paper is long enough to make your 2 tick marks. Note that this method works better for shorter line distances. Hold the edge of the paper still on the map and mark as accurately as possible where the paper lines up to your 2 points.
For instance, a common topo map might have a 1:100,000 scale, where 1 centimeter equals 1 kilometer. [1] X Research source The bar scale may also contain a primary scale, which shows whole units increasing from 0, left to right. There’s also an extension scale, which shows fractions of a unit increasing from 0, right to left. Use this method if you have a short distance between your tick marks that easily fits within the given bar scale.
Where you line up the right tick mark on the primary scale depends on what it takes to fit the left tick mark onto the extension scale. Keep the right tick mark on a whole number. The whole number the right tick mark is on indicates that your ground distance is at least X-many meters/kilometers/miles as the scale indicates for that number. You’ll find the rest of the distance more precisely with the extension scale.
The segments on the extension scale are typically small rectangles, alternately shaded and unshaded for easy reading. You can guesstimate at even smaller increments by visually dividing each rectangle into 10ths 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 the right tick mark on the 3 mark, you have at least 3,000 meters in your measurement. If the left tick mark falls on the rectangle in the extension scale that indicates 900 meters, you’ll have an additional 900 meters in your measurement. Your total measurement would then be 3,900 meters.
Hold the piece of paper still and evenly against your two points in order to make the most accurate tick marks. If you want to, you can use a ruler or tape measure straight on the map, and note down the measurement to the smallest fraction of a unit possible.
If measuring with centimeters, find the distance to the nearest millimeter. If using inches, find the distance to the nearest eighth of an inch. Note the scale given at the bottom of the map. It should show a ratio and a bar scale in both centimeters and inches. If one equates to a whole number, like 1 centimeter = 1 mile, you might choose that unit for easiest measuring.
For example, for a map with a scale of 1:10,000: If you measured 10 centimeters from your Point A to Point B tick marks, you would multiply 10 by 10,000 to get 100,000 centimeters, the true ground distance from Point A to Point B. [2] X Research source You can then convert your number to a more relevant distance. 100,000 centimeters equals 1 kilometer, for example, which is about 0. 62 miles. [3] X Research source
To use the bar scale for a longer measurement, place the right tick mark on the farthest number on the primary scale. Make another mark on your paper where the extension scale ends on the left, and note this distance. Use your new mark as the right tick mark and measure using the bar scale as normal. Add this to your previous number to get the total distance. If you are measuring the distance between your tick marks or 2 points on a map using a ruler that is not long enough, try a tape measure for more length.
Use a piece of paper to mark the distance on the map. Measure several straight lines along the curved routes and add them together. For the greatest accuracy, measure a greater number of smaller straight lines along a curved route. [4] X Research source
Use a piece of paper or a ruler to measure the distance between point A to the edge of the map. Add the distance the marginal information of the map gives to the desired town or highway to get the total distance. Be sure that your units of measurement are the same before you add the two distances.
