Map Scales...Say What! ©

 

 

Map scales, photograph by the Author.

Did you ever give much thought to those bars and numbers on the bottom of your map?  Probably not.  Most people don’t pay much attention to the scale of a map, or really understand it.

 

“So, what do those bars and numbers mean”, you might ask, and “what map scale is the best to use when travelling in the wilderness”?

Great questions! 

 

Larger is smaller...

 

Excerpts from Staying Found, by June Fleming, from pages 30 and 31.

 

To be of any use at all, a map must show the locations and distances of places accurately, all while shrinking the real world down to a convenient to hold, use and carry, piece of paper.  To do this, everything on the map must be drawn proportionally smaller than it is in the real world.  The proportion chosen for a map is its scale. 

 

The scale from my 1978 Algonquin Provincial Park Canoe Routes map, showing both a bar scale and representative fractions, photograph by the Author.

Simply put, the scale of a map is the relationship between the distance on the map and distance on the ground in the real world.  A map scale might be shown as a graphic scale or a bar, or it might be given as a “representative fraction”, where one unit of measurement (either an inch or a centimeter) on the map represents a larger number of the same units on the ground.  For a map scale of 1:62,500, an inch on the map represents 62,500 inches or almost one mile on the ground.¹  The first number in a representative fraction is the map distance and it is always 1.  The second number, which is the ground distance, is a larger number, and the larger this second number, is the smaller the scale of the map is, so larger is smaller!²

 

The two map scales which are most useful to travelers in the wilderness are the 7.5-minute map, also known as a “7.5-minute quadrangle” map, and the 15-minute map.  The 7.5-minute map has a scale of 1:24,000 and covers 7-½ minutes of latitude and longitude, or an area of about six by nine miles, and with this scale just over 2-½ inches on the map equals a mile on the ground.  Topographic map coverage for the United States has been completed at this scale and most areas have maps of this scale available.³ 

 

The 15-minute map has a scale of 1:62,500 and maps 15 minutes of latitude and longitude, or ¼ of a degree, this is an area of about twelve by eighteen miles, and 1 inch on the scale equals about one mile on the ground.⁴

 

The differences between map scales, an excerpt from “Map Scales”, by the U.S. Department of the Interior, found HERE.

 

So, which one do I choose?

 

A 7.5-minute map shows only a quarter of the area of a 15-minute map, but it is easier to read and shows more detail, which might be useful when travelling through rugged terrain.  One big problem with this size of map scaling is that if you are looking for a landmark which is more than a few miles away, it might not be on the map!  A 15-minute map shows less detail than a 7.5-minute map, but it covers more area and includes more landmarks.

 

Robert S. Owendorff, who was the inventor of the “Shadow-tip Method” of direction finding, felt that 7.5-minute maps, with their scale of 1:24,000, were the best for wilderness travelers to use, because they show more detail than the 15-minute maps.  He did feel that you could use the 15-minute maps for wilderness travel if you were willing to give up on the extra terrain detail.

 

June Fleming, the author of Staying Found, thought that the solution to the 7.5 or 15-minute map dilemma was to use both maps.  She suggested that you use the 7.5-minute map (1:24,000 scale) for your main area of travel and that you use a 15-minute map (1:62,500 scale) or even a 1:250,000 scale map as an overview, to get “the big picture” of the terrain and the landmarks.

 

An excerpt from Staying Found, by June Fleming, from pages 32, who notes some of the thinking that you will have to do to determine which map scale is the best for you.

Ultimately the decision will come down to what maps are available for the area that you are travelling through.  If the scale that you want is available, great!  If not, then you will have to make do with a different scale of map.  If the are that you are traveling through is mapped in both the 7.5-minute and 15-minute scales, even better, you can either choose to bring one or even both scale sizes.

 

So, next time you look at a map, look down at the legend and see what scale it is, because now those bars and numbers will mean something to you.

 

Don’t forget to come back next week and read “You’re Going Canoeing...But What About Your Feet!  ©”, where we will talk about what to wear on your feet when you are canoeing.

 

I hope that you continue to enjoy The Woodsman’s Journal Online and look for me on YouTube at Bandanaman Productions for other related videos, HERE.  Don’t forget to follow me on both The Woodsman’s Journal Online, HERE, and subscribe to BandanaMan Productions on YouTube.  If you have questions, as always, feel free to leave a comment on either site.  I announce new articles on Facebook at Eric Reynolds, on Instagram at bandanamanaproductions, and on VK at Eric Reynolds, so watch for me.

 

That is all for now, and as always, until next time, Happy Trails!

 

 

Notes

 

¹ 62,500 inches divided by 12, equals 5,208 feet or, .986 of a mile.

 

³ "The larger the number, the smaller the scale" sounds confusing, but it is easy to understand. A map of an area 100 miles long by 100 miles wide drawn at a scale of 1:63,360 would be more than 8 feet square! To make this map a more convenient size, either the scale used or the amount of area included must be reduced. If the scale is reduced to 1:316,800, then 1 inch on the map represents 5 miles on the ground, and an area 100 miles square can be mapped on a sheet less than 2 feet square (100 miles at 5 miles/inch equals 20 inches, or 1.66 feet). On the other hand, if the original 1:63,360 scale is used but the mapped area is reduced to 20 miles square, the resulting map will also be less than 2 feet square.”

 

From “Map Scales”, by U.S. Department of the Interior

 

³ “The U.S. Geological Survey publishes maps at various scales. The scale used for most U.S. topographic mapping is 1:24,000. Maps published at this scale cover 7.5 minutes of latitude and 7.5 minutes of longitude; they are commonly called "7.5-minute quadrangle" maps. Map coverage for the United States has been completed at this scale, except for Puerto Rico, which is mapped at 1:20,000 and 1:30,000, and a few States that have been mapped at 1:25,000. Most of Alaska has been mapped at 1:63,360, with some populated areas also mapped at 1:24,000 and 1:25,000.”

 

From “Map Scales”, by U.S. Department of the Interior

 

⁴ The exact amount of coverage depends upon the latitude, the closer to the equator, the more square miles the map covers.

 

From Staying Found by June Fleming.

 

 

Sources

 

Fleming, June; Staying Found, [Vintage Books. A division of Random House, New York, NY, 1982], pages 16 and 30-32

 

Owendorff, Robert S.; Better Ways of Pathfinding, [The Stackpole Company, Harrisburg, PA, 1964], page 18

 

U.S. Department of the Interior, U.S. Geological Survey, Earth Science Information Center (ESIC), “Map Scales”, https://pubs.usgs.gov/unnumbered/70039582/report.pdf, accessed May 27, 2020