How to Calculate Travel Distances Between Cities

How to Calculate Travel Distances Between Cities
Accurately determining the distance along an overland route is an integral part of trip planning. The most usable representation of the surface of the Earth is a map. Maps are planar projections of the curved surface of the Earth. This distorts distance, direction, shape, area and scale represented on the map. Maps of relatively small areas of the Earth can preserve greater accuracy of these attributes than maps covering larger areas due to the reduced distortion caused by the curvature of the Earth. Another consideration is scale. On large maps, scale is dependent on location, and maps of large areas will often include differing scales for different areas of the map. Even with these limitations, many maps will still allow a fairly close approximation of the distance between cities. Globes avoid these projection issues but may be cumbersome and sacrifice much detail.

Instructions

Difficulty: Easy

Things You’ll Need:
  • Map or Globe String Tape
  • Map or Globe
  • String
  • Tape
Step 1
Select a map that best preserves the scale, distance and shape between the desired locations. A useful strategy is to select the map that covers the smallest area and greatest scale possible. A state map is preferred over a national map if the points lie within the state. Topographic maps would be preferable to state maps if both points lie within one map or on adjoining sheets.
Step 2
Locate the starting and ending destination for your route on a map. Also locate the scale in the map legend.
Step 3
Place a string at the starting point of the route. It may be helpful to use a small piece of tape to hold the string in place.
Step 4
Align the string along the route to be taken. Follow any bends and curves in the road or trail. For long, winding routes additional tape may be needed to hold the string in place. Alternatively, segment the route into smaller, more measurable increments but beware of compounding errors. A 1-kilometer error made 10 times becomes a 10-kilometer error.
Step 5
Once the string has been laid out across the route from starting city to destination city, mark the string at the beginning and end. Remove the string from the map and align along the corresponding scale in the map legend. If the string is longer than the legend, measure the string in segments, again being mindful of compounding errors. Another approach is to measure the length of the string using a ruler. Then measure the distance represented per inch or centimeter using the scale in the map legend. The distance is then calculated by multiplying the length of the string in inches or centimeters by the distance represented by each inch or centimeter. For example, if the string is 11 centimeters long and each centimeter represents 10 kilometers, then the route measured is 110 kilometers.
Step 6
Repeat your measurement to verify the accuracy of the results.

Tips & Warnings

 
Keep in mind significant figures. For example, the number "2" represents all numbers between 1.5 and 2.4. The number "2.0" represents all numbers between 1.95 and 2.04. This slight error in the measurement is accounted for in your calculations. In the above example, the 110 kilometers can have only two significant figures and therefore represents a distance between 105 kilometers and 114 kilometers.

Article Written By David Chandler

David Chandler has been a freelance writer since 2006 whose work has appeared in various print and online publications. A former reconnaissance Marine, he is an active hiker, diver, kayaker, sailor and angler. He has traveled extensively and holds a bachelor's degree from the University of South Florida where he was educated in international studies and microbiology.

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