BEST MADE PROJECTS

Cartographic Scale, by Bill Wetherholt, Best Made Guide to Cartography

Greetings from North Dakota: where the land is stirring and cabin fever is at an epidemic level. You can sense the change of the season in the wind, as less arctic air pours into the northern plains, and I have found myself lingering on maps as I mentally plot my next adventure. This increase in carto-lust is not absent with the rest of the gang at BMC either, nifty maps are available now! While we are dusting off old maps and snagging new ones, it felt appropriate have a brief chat about scale.

The majority of maps you will ever encounter are smaller than the reality they represent, and scale will inform you how much smaller. Scale describes the ratio of the distance on a map, globe, model, or profile to the actual distances they represent.  There are three ways in which scale can be represented in your map: with a representative fraction (1:100,000), a verbal statement (1 inch equals 4 miles), or in a graphic bar scale. For instance, if your sweet new BMC topographic map’s scale is 1:100,000, that means one unit of distance on the map is the same as 100,000 of that same unit on the surface of Earth, whether inches, centimeters, etc. And, for the record, 1 inch equals about 1.6 miles at a scale of 1:100,000 (for the math dorks: there are 63,360 inches in a mile, so 100,000/63,360 = 1.6).

Now what about the terms large-scale and small-scale? You have likely heard these terms, however, the two are commonly confused with each other. A large-scale map shows a large amount of detail over a geographically small area. A small-scale map shows a small amount of detail over a geographically large area. Think of the size of the representative fraction: a 1:24,000 scale would be large, whereas a 1:1,000,000 would be small; 1/24,000 is a much larger number than 1/1,000,000.

Finally, when considering scale, remember that a map is a generalization of reality and certain information is suppressed so your map is easy to read. A good map uses symbolization that makes sense (triangles for mountains, religious symbols for their respective houses of worship, and so forth). The smaller the scale of the map, the greater the generalization will be. Think about how much information you can communicate on a globe (small-scale) compared to a regional highway map (medium-scale) compared to a county map (large-scale). Scale directly impacts the amount of information a map can effectively convey to its audience. Anyone who has read Bill Bryson’s account of through-hiking the Appalachian Trail in A Walk in the Woods can appreciate this concept:

“I dumped my pack and searched through it for my trail map…[The maps] vary somewhat, but most are on an abysmal scale of 1:100,000, which ludicrously compresses every kilometer of real world into a mere centimeter of map.  Imagine a square kilometer of physical landscape and all that it might contain—logging roads, streams, a mountaintop or two, perhaps a fire tower, a knob or grassy bald, the wandering AT [Appalachian Trail], and maybe a pair of important side trails—and imagine trying to convey all that information on an area the size of the nail on your little finger.” (pp. 73 – 74)

So the next time you are planning your trip, remember to incorporate a map that has an appropriate scale so that you don’t run into an issue like Mr. Bryson. Don’t forget the differences between a small-scale and a large-scale map, and remember that every map is a generalization of reality no matter what the scale. Think Spring!