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Convergence–Is this diagram right?
Posted by bill93 on April 3, 2023 at 12:38 amI was looking at something in McEntyre’s book and noticed this diagram. True, the main point of the diagram wasn’t convergence, but I’m confused by where the standard corners and closing corners are.
Can somebody straighten me out – what is the scenario that results in the closing corners being west of the standard corners? Isn’t it usually the other way?
NotSoMuch replied 1 year, 5 months ago 5 Members · 8 Replies -
8 Replies
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The diagram shows the sections east of the principal meridian.
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They can go either way. The offset gradually changes. Two standard parallels fall in my most frequent work area. One is about a quarter mile offset. The one 30 miles to the north is very close to a half mile offset.
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I don’t see that being east of the principal meridian has any effect here. The standard corners were marked along a township line, and now we’re subdividing within that township, wherever it is.
Yes, of course the offsets can be anything as you move along a standard parallel (called a correction line in Iowa).
If the NE corner of the township nearly matches the SE corner of the one to its north as shown, then the closing corners on the township line should be a few feet east of the standard corners by the time you get across the township, plus or minus some random measurement error that could be more than a few feet.
I’ve concluded there was little thought put into the diagram other than its purpose of showing the order of marking the lines. All the lines within the township are as near perfect as I can measure on the figure, and those along the township lines vary more than that. In real life it would be nearer the reverse because the standard corners were directly measured and the closing corners accumulated error over distance.
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The east line of the townships east of the prime meridian are all true north and converge towards the prime meridian, lessening the north line of that township. The closing corners will fall west of the township corners to the north which were all laid out at half mile intervals along the township line from the prime meridian (or guide meridian).
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I see now.
This shows closing corners on both north and south lines. They would only have those if one of the lines was a standard parallel, right? Wouldn’t be both lines.
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Adding this photo for fun while discussing how things were laid out. Note the huge sections that are created along the west line of Range 8 East of the 6th P.M. This is a bit more than 40 miles east of Wichita for those who want to take a better look. The north line of Township 26 South is the Fifth Standard Parallel south of 40 degrees North latitude and the north line of Kansas. Note where the northeast corner of Section 1 falls.
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Here is a better view of the area:
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This shows closing corners on both north and south lines. They would only have those if one of the lines was a standard parallel, right? Wouldn’t be both lines.
Yeah, that’s some legitimate sloppiness in the diagram.
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I’ve concluded there was little thought put into the diagram other than its purpose of showing the order of marking the lines. All the lines within the township are as near perfect as I can measure on the figure,
I believe that diagram is meant to be a schematic, simply to show corner naming and marking conventions. I wouldn’t attempt to “measure” anything off that diagram.
Jeff D.
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