Dictionary of Altitudes

I was in the library at work looking for a German/English chemical dictionary when this book caught my eye: A Dictionary of Altitudes in the United States, 4th Edition, by Henry Gannett. The book was published in 1906 by the Government Printing Office in Washington and contains tables of altitudes organized by state and city. As a private pilot, I think a lot about altitudes but they are so easy to obtain you take them for granted. Charts are loaded with them, planes have reasonably good altimeters, and GPS with WAAS capability will give position and altitude with an error of roughly 20 feet. I did a little digging to understand what was behind the altitude dictionary.

Gannett started with the US Geological Survey around the time it was founded as a separate agency in the Department of the Interior. He was chief geologist about the time that then director John Powell got the blessing of Congress to continue preparation of a geological map of the US. In that period, the topographic mapping effort received the bulk of USGS funding. Gannett was a founding member of the National Geographic Society and one of its presidents. You can find a short entry on Gannett here and a nice overview of the USGS here. Besides the general desire to understand US geology and geography, a lot of folks needed altitudes. For example, railroads planned paths to minimize grades, the military needed terrain information for strategic planning, and topological information helped determine watersheds.

The Dictionary of Altitudes has a short methods section describing how they measured the altitudes. Many were based on barometric pressure readings and a fair number mentioned using trigonometry. Some altitudes were based on measuring the boiling point of water. This website has a great discussion of how altitudes were measured in the 1800s. It also discusses why different methods were used and the limitations and errors in the measurements. Quite a good read.

I checked a few of the measurements to get an idea of accuracy. It’s amazing how good the values are! For Little Falls, Minnesota there were two entries. The first was for the Northern Pacific Railroad (1120 feet) on the east side of town and the second was for a square cut on a step at the entrance to the Buckman Hotel (1114 feet). The Hotel was still operating when I was growing up. I wonder if there is a USGS benchmark there (here is an example). If there is, I walked past it hundreds of times as a kid and didn’t even notice it or know about the effort involved in placing these markers.