Friday, July 27, 2007

How Elevation is Determined

The local librarian did not fail me!

The college librarian did not immediately know how elevation is determined, nor did she know exactly where to look to find out. The encyclopedias had nothing, which is particularly distressing when you consider how much information is in the Britannica Macropedia!

However, librarians are diligent researchers, and she did find Cecil Adam's Straight Dope.

There we learned:

"This is not the scientific process you might think. As far as I can tell nobody publishes an official list of elevations for cities in North America. Highway departments, mapmakers, almanac compilers, and what all come up with numbers for their own purposes, but they use different sources, and their figures don't always agree. . .

"Town elevations may be the altitude at some prominent public place (Caltrans uses city hall) or they may be an average for the downtown area. Either way they're often just estimates. Caltrans got its numbers from the U.S. Geological Survey, but the USGS got them by eyeballing the contour lines on maps. . .

"It's only when we get into the no-nonsense world of engineering that we start to get some precision. Many big towns have established a "city datum," a standard elevation pegged to some known point, which is used in blueprints for major construction projects. For instance, on a drawing for an office building, the elevation of the sidewalk in front of the entrance may be marked as "+15' Podunk city datum."

There you have it.

Is Cecil Adams credible, you ask. He/she certainly is. They have never been known to be wrong, except when they are. Moreover, the column is named "The Straight Dope," and who would risk that on a fraudulent answer to my simple question.

The next question is, is there are city datum for Lindsborg, and if so, where is it. I will ask on Monday!

The image in the upper left corner, by the way, is from the Library's extensive collection of G. N. Malm artifacts.

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