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Making Waves: Episode 102 (July 26, 2012)

This is Making Waves from NOAA’s National Ocean Service. I’m Troy Kitch. 

Have you ever been to Four Corners? It’s the only place in the U.S. where four states meet up…Arizona, New Mexico, Colorado, and Utah. A few years back, there was some confusion over the position of a monument at Four Corners that marks the spot where the four states meet. Some reports claimed that the position of this marker was off by two and a half miles. Today, we’re revisiting a 2009 interview with Dave Doyle, chief geodetic surveyor from NOS’s National Geodetic Survey. As you’ll hear, Four Corners is exactly where it’s supposed to be – and the reason for that is that surveying isn’t only about taking precise measurements with sophisticated equipment, it's also about history, technology, and law. Enjoy!

So here's the problem: there's a widely held misperception that the boundary between Colorado and Utah – the line of longitude – is 109 degrees West from Greenwich, England. As you might remember from your school days, longitude lines are the ones that stretch from the North to South poles.

Greenwich, England is where the Prime Meridian is. It's zero degrees, the reference point from which everyone today measures how far East or West they are. Note that I said 'everyone today' has adopted Greenwich as the Prime Meridian. It hasn't always been that way, as you're about to find out.

Now imagine you trek out to the desert to visit Four Corners with a handheld GPS receiver. At the site, you check your position. You expect it to read 109 degrees West. But it doesn't. It reads 109 degrees plus a little more. What gives? Well, it turns out that the boundary between Colorado and Utah – the line of longitude - wasn't measured from Greenwich when it was recorded back in the 19th century. And it's not – and never has been – at 109 degrees West.
We asked Chief Geodetic Surveyor Dave Doyle of NOAA's National Geodetic Survey to explain:

[Dave Doyle] "The reality is that that was never the definition of the Western boundary of Colorado, [or] the Eastern boundary of Utah. It's actually defined as being 32 degrees longitude West of the Washington meridian, Washington referring to the city of Washington, DC. And the meridian referenced in that statute is now what we refer to as the Old Naval Observatory, in downtown Washington, DC. The Old Naval Observatory has a longitude that is not exactly 77 degrees West of Greenwich. It's 77 degrees, three minutes, and, depending on how you define it, four -- almost five -- seconds. So when you add 32 degrees to that, you should come up with 109 degrees, three minutes, and roughly five seconds. And that three minutes and five seconds of longitude is roughly two and a half miles. And that's where we believe the original discrepancy came from. Someone believed it should be 109 degrees longitude, when that was never how it was statutorily defined."

And this is where the misunderstanding comes from. The longitude of the position of the Four Corners monument is based on a measurement taken in 1875, and the reference point used was in Washington, DC. This was before the Prime Meridian was adopted as the standard of measurement by the whole world.

[Dave Doyle] "It was very common at that time for countries or small groups of countries to have their own local longitude orientation. So the French had the Paris Observatory, the British used Greenwich, the Germans used Potsdam…and on and on. So we had our own national meridian."

Now, if you use today's modern tools to measure that distance from the Old Naval Observatory to the Four Corners boundary, you would find that the position of the monument is off just a bit, somewhere between 1350 and 1800 feet. That discrepancy is because the tools used in 1875 were not as accurate. And, to a lesser degree, there's also a slight variation depending on where and how you measure from the Old Naval Observatory. Doyle said that this is a common, everyday issue in the world of surveying:

[Dave Doyle] "Many, many, many of the parcels that everybody occupies everyday are defined by descriptions, that is directions and distances, that in some cases go back several hundred years, and were measured with technologies 200 years ago that were in no way comparable to current technologies. So, it's not at all unusual to find distance, or direction or, in this case, a coordinate that is in some cases, significantly different if we had been given the luxury 200 years ago of doing this with contemporary technology such as the Global Positioning System."

So now you might be saying to yourself, 'Aha, so the monument isn't in the right spot after all.' But actually it is. And this is the last piece of the puzzle. Even though the marker is not exactly 32 degrees West of the Naval Observatory when measured with today's tools, that's now irrelevant. And that's because the four states that make up the Four Corners all agreed long ago that the monument, well, marks the spot. This is what's important to keep in mind about surveying: it's about precision and science, but it's also about history and statutory law. Doyle said that the original 1875 surveyor, a man named Chandler Robbins, got it right. The Four Corners monument is exactly where it's supposed to be:

[Dave Doyle] "It's in its true location. It's exactly where the surveyor at the time placed it. Given the technology that he enjoyed, given the conditions that he had to work under, Mr. Robbins placed that monument exactly where he was directed to, which was 32 degrees West of the meridian of Washington. What he lacked was the contemporary surveying technology that we have today. So in his mind, and based upon all of his observations, and his calculations, he placed the monument exactly 32 degrees longitude West of the Naval Observatory. And that is exactly where it should be, even though its numerical difference today might differ by 1800 feet, or perhaps even if it were two and a half miles, it would become irrelevant, because the monument has subsequently been accepted by all four states as defining the legal boundary, and therefore, it is the monument of record, and in surveying monuments control."

That’s all for this week. We’re going to take a brief summer recess after this episode. We’ll be back with the next Making Waves on August 23.

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You’ve been listening to Making Waves from NOAA's National Ocean Service. We’ll be back in two weeks.