Border Slash - Is it Really the 49 Parallel? (转贴)

dida · 发表于 2006-5-28 13:26:13

The Border slash from the Border Cairn on Hozomeen Ridge

Subject Area: Manning Provincial Park

For hundreds of kilometers, the border between Canada and the United States runs along the 49th parallel, and is marked by a huge slash through the trees. However, which 49th parallel? As you may know from your GPS, the location of both lat-long and grid references can vary 200 meters, depends on which map datum you use. So we measured where the cairn was located, marked it as a waypoint, and then read out the location in different datums.

  NAD27 (Canada): 49:00.025-120:59.970  WGS84:       49:00.017-121:00.044

Note that both of these measurements indicate that the cairn is actually located within Canada.
The question is: what is the true definition of the border? Is it on the 49th parallel according to the Clarke Ellipsoid of 1866, which many of the US maps refer to? I don't know. The 1 meter high aluminium border cairn on Hozameen Ridge contained the following inscription: Treaty of 1846. Line established 1857-1861. Surveyed 1908-1907. So whatever is written down in the treaty between Britain and USA could not even have referred to North American Datum 1927. It is probable that the wording of the treaty left room for corrections due to survey errors, it would be interesting to know what provisions were made for continuing refinements to the ellipsoid model of the earth. I would guess it was probably worded such that id doesn't change it as newer map datums become available. Otherwise the border slashes are in the wrong location.

Since I posted the original photo essay, Mike Cleven says: The treaty has the interesting wording 'the border as surveyed" or something to that effect in whatever legalese of the day; i.e. the border is NOT the 49th parallel of latitude, but the line _surveyed_ along it by the Boundary Commission. This wasn't so much a clever ruse, supposedly on the part of the Americans (who did take advantage of it in various places, notably the "Angle" on Lake of the Woods in what is now Minnesota but "should" have been Canada), as a recognition by official geomancers that their survey lines were NOT astronomically accurate, and that there would necessarily be the occasional miscalculation because of equipment error (this was the excuse with the Angle and occasionally elsewhere, although after that first debacle the Canadians were a bit more careful in checking the measurements). So the upshot is that wherever the survey parties cut the line and laid cairns IS the boundary; not the 49th Parallel as such.

  - this issue made the news again recently in the wake of satellite surveys which showed that there's a few hundred sq km differential all the way along between Lake of the Woods and the Gulf of Georgia. A few dozen metres of Whatcom County "should" be part of BC, including the US border stations at Point Roberts; but east of the Cascades the opposite is true, but not by so much; there are a number of deviations across BC's boundary, and even more across the Prairies (where you'd think it would have been easier to plot a straight line, but....). Totting the variations up along the line, IIRC the US got the better of it by a certain percentage (something like 700 sq km to them, 400 to us, leaving a 300 differential or something like that) but we have quite a bit of what "should" be theirs; notably along the Alberta-Montana boundary for some reason. It only takes a few metres error in the latitude calculation across several dozen kilometres to make up more than a few sq km, remember.

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