Contour Intervals for Dummies, the Rewrite Redux

Some symbols on USGS Topo Maps

Today marks a "quantum leap" in our staff's wanderings through the content of the erstwhile eHow.com: we'd already found content that Leaf Group sent to the "cleanup team."¹ This, however, is the first time that we found a rewrite of a rewrite! A long time ago, serial DotD Soren Bagley attempted to explain "How to Calculate Contour Intervals," a job so... sloppy? clueless? that Soren's prose was overwritten by an attempt by one Karen G. Blaettler.² Guess what: apparently, someone at Leaf Group follows this blog, because Karen's attempt only lasted a little more than a year before they called in Kevin Beck.

They shouldn't have bothered...

It didn't take much time for our staff expert on contours, a guy who by a conservative estimate has generated several tens of thousands of contour maps, to see that Beck, or KeMiBe, as he styles himself, was lacking in the accuracy department:

"Contour lines are spaced by contour intervals and represent areas on land that lie the same distance above sea level..."

No, Kevin, they aren't "areas": a line can't represent an area! A contour line connects points of equal elevation! But enough of that: clearly, Leaf Group has relaxed the 300-500 word limit eHow had imposed, because Beck expanded this topic to more than 1200 words (the site must pay by the word these days). In truth, there are three possible answers, two easy and one hard, to this question.

1. If you're looking at a map, find the legend: a competent cartographer will include the contour interval there. No idea what KeMiBe would do...
2. If you're looking at a map and there's no legend, do the math. Why is that so hard to say?
3. If you're making a map and want to calculate a suitable contour interval, you need to take into account the range of the data, the size of the map, common contour intervals for this data type, and the complexity of shapes. It's an art, which is probably why Bagley, Blaettler, and Beck all blew it.

Some of Kevin's other blather rubbed our mapper the wrong way, including (but not limited to):

"...5,280' is the altitude of downtown Denver, Colorado, USA..."

In point of fact, it's not: 5,280 feet was the elevation of a marker 15 feet or so from the sidewalk on the wall of the old Denver Post building on 15th Street, but downtown slopes continuously toward the confluence of Cherry Creek and the South Platte River.

"...topographical [sic] maps show details... that are absent on traditional street maps... many of these are aimed specifically at hikers, runners and other purposeful explorers rather than motorists..."

Utter bull: topographic maps are not aimed at "purposeful explorers," moron! They're intended to show every available detail; which is why they include such information as the location of roads, power lines, wells, orchards, schools, churches, post offices... That's what makes them so valuable to people who know how to use maps! And then there's,

"Often, index points are given along with index contours. For example, the precise elevation of a mountain peak is given even when it does not correspond with a contour line."

It's a shame that no one told our Dumbass of the Day about the benchmarks. If they had, he might not have said something so uneducated. Oh, well... and by the way: shame on Lana Bandoim, B.S., for her sloppy review.

¹ Not always successfully, as is documented in our "Failed Rewrites" collection.
² Find our send-up of Soren's attempt here, and of Karen's try here.

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