American Meridian

The international community recognizes a prime meridian that runs through the Royal Observatory at Greenwich in southeast London, England. It serves as a reference point for universal time and distance. However, that has not always been the case.

Latitude is easy. The equator divides the planet into northern and southern hemispheres quite logically. Longitude is arbitrary. Any spot can separate eastern and western hemispheres, and indeed, many spots have been selected for that honor and later discarded.

It’s not quite that simple if one expects the meridian to have any meaning. Any spot can be chosen but it has no purpose if people don’t recognize the resulting meridian and use it. This was particularly daunting in the nineteenth century when almanacs full of stellar calculations had to be published each year to support shipboard navigation. Only the wealthiest and most influential of nations could afford the luxury of maintaining a global meridian, countries like England and France, or nations seeking acknowledgment of their growing ascendancy like the United States.

The United States had no less than four meridians running through various points of significance within its capital city, Washington, DC: the Capitol Dome; the White House, the dome of the Old Naval Observatory and the clock room of the New Naval Observatory.

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The most significant of the four was probably the American Meridian which ran through the dome of the Old Naval Observatory, shown above. Its heyday stretched from about 1850 when it first emerged from Congressional legislation until about 1884 when an International Meridian Conference selected Greenwich as a universal standard. The American Meridian continued to exist until its eventual repeal in 1912 but by then had lost much of its practical usefulness. Thus the American Meridian served as a viable reference point only for about thirty-five years.

It wasn’t used for navigating the seas since Greenwich worked fine even for American sailors, however it provided genuine usefulness for another purpose — land surveying. The accuracy of nineteenth century surveying decreased as one moved further away from the common reference point. The United States was in the midst of carving out vast interior spaces into territories and states, and could not depend on a meridian on the other side of the Atlantic Ocean.

American Meridian in Washington, DC

The American Meridian may not have lasted very long but it coincided with a vital cartographic period in United States history.

View American Meridian in a larger map

Notice the prevalence of vertical lines of longitude drawn into several of the western states. Many of their borders follow whole integers of the American Meridian.

Failure to understand its existence sometimes leads to gaffes. There were widespread reports in April 2009 that the Four Corners marker had been placed in the "wrong" location. Actually it was located on the correct spot. The media, either not realizing or not bothering to examine the history of the American Meridian, had relied on the Greenwich Meridian by mistake.

While the American Meridian retains a legacy through the lines of longitude defining several of the United States, very little remains to commemorate the discarded prime meridian in Washington, DC today. The Old Naval Observatory now serves as the headquarters for the Navy’s Bureau of Medicine and Surgery. Public visitors cannot visit the observatory building, nor can they even access its grounds which are secured by armed guards and fences as part of protecting federal government facilities in the modern age.

Plaque Commemorating American Meridian

Travel a few blocks due north however, and a tiny marker exists at the southeast corner of 24th & H Sts., NW, on the campus of George Washington University. The invisible line runs right through the university, cutting through some of its buildings such as New Hall and Ross Hall. The university recognizes its unique straddling of the old meridian and has included it in their "GW and Foggy Bottom Historical Encyclopedia."

It’s not Greenwich but it’s the closest thing on this side of the Atlantic.

5 Replies to “American Meridian”

  1. There’s also a visible marker denoting the White House meridian: the small Jefferson Pier stone located at the intersection of the axes of that meridian and the latitude of the Capitol dome, a conveniently short walk west and just north of the Washington Monument. It’s hard to see unless you’re looking for a smallish white stone sticking up, but it’s there. It disproved my mistaken notion that the Washington Monument was directly on the Capitol dome parallel.

    Also, for the Four Corners monument, isn’t it sort of (pedantically) absurd to talk about it being mis-surveyed, even IF the surveyors had missed the intended spot? Whatever they mark as the boundary is accepted as correct by definition, no? Hence the small jogs all along the borders of the right-angle states.

    One more, completely unrelated, but I just came across this and I wondered if you had tackled the subject before: there are three (quite small) airports whose runways either lie along or cross the US-Canada 49th-parallel border: Piney Pinecreek Border Airport, Avey Field State Airport, and Coronach/Scobey Border Station Airport. One wonders what the customs and immigration situation is for those places.

    Thanks for another great DC-centric post; I always love them. DC and the surrounds seem to be a particularly dense repository of geo-oddities.

  2. There are other meridians as well in North America, if not global in nature. In Canada there are six prairie meridians that all townships and land holdings are measured from.

    Some pretty good information here:

    It is amazing how an arbitrary line can have such an effect on the lives of so many people.

  3. I assume you have read “The States and How They Got Their Shapes” by Mark Stein? (

    Not totally accurate (he totally messed up the history of “the Wedge” in Delaware), and short on detail, but a good introduction to the though process behind our borders.

    Stein spends a good amount of time discussing the “square states” and the goal of trying to keep them about the same size, but he doesn’t mention the role of the American Meridian. Thanks for the additional information!

    1. Greg: A very insightful response, as usual. I think the stone you mentioned is on the same meridian as the Zero Milestone at the northern edge of the ellipse. It’s generally on my tour when friends and family visit; a tour of all sorts of oddities, geographic and otherwise, although I throw in a couple of museums just so they don’t think I’m a total nutcase. DC does seem to have more than its fair share of idiosyncrasies, or maybe there is some selection bias on my part, so I’m trying to spread them out a little. I actually visited the American Meridian the same day I visited the DC Highpoint several months ago but waited a little while to post the article so readers don’t get tired of all that DC content. Correct on the absurdity of the supposed straight-line borders. They’re accepted now in spite of all the little anomalies surveyed into them. Oh, and I had no idea about the airports. Very cool. I too wonder how they operate now that passports are required for U.S. citizens visiting and returning from Canada. And speaking of Canada…

      Hamish: You’ve brought a couple of great Canadian examples to my attention recently and I sure wish I could provide more Canadian content (I do have some, but not as much as I’d like). If you have any glaring examples that I’m missing, please send me a note off-line and I’ll see what I can do to cover some of them in future posts, with full credit to you of course. There were a bunch of other meridians and points used in the USA too, and here’s a page that links to images of those Principle Meridians and Base Lines. I was fortunate to visit the one for Wisconsin (the Point of Beginning) a couple of years ago.

      Bill: Thanks for the book recommendation. I haven’t actually read it yet although I knew it existed. I’m hoping to find the time someday.

  4. Oh, of course, the Zero Milestone. I somehow forgot about that. Speaking of meridians, the Michigan Meridian has what I suspect to be the unusual property of being defined from a base point that is not in Michigan. Instead, it’s defined northerly from the confluence of the Auglaize and Maumee rivers in Defiance, Ohio (very close to where I used to live, which is why I know about it). The base point is also not within the once-disputed-between-Michigan-and-Ohio Toledo Strip that’s now part of Ohio; it was always part of Ohio. Why they chose it as opposed to a point in Michigan itself, I don’t know, except that there was a military fort at that location already and the resulting meridian did run almost the full length of mainland Michigan before going into Lake Huron.

    Then again, maybe many such meridians or baselines are defined by points outside (and not adjacent to) the state(s) for which they’re drawn. It just seems unusual to do so.

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