I am a leyperson and wondering.. Is it unusual for surveys to be based on magnetic north as opposed to true north? An adjacent neighbor had a survey done and it seems to jive out (roughly) using a good compass based on magnetic north. I called the surveyor to ask some questions, but did not ask this question. They had indicated that this survey did not use GPS because "it was not used at the original time of the mapping". Rather it used metes and bounds. (The original development mapping was done about 40 years ago).
Is that unusual to use MAGNETIC north? Any help would be greatly appreciated.
No, it is not unusual. Probably less common these days with the proliferation of GPS equipment. Oftentimes, a survey might be oriented to match the north orientation of an earlier nearby survey, which may or may not be based on magnetic north.
Thank you kindly. ?????ÿ
I am a leyperson and wondering.. Is it unusual for surveys to be based on magnetic north as opposed to true north? An adjacent neighbor had a survey done and it seems to jive out (roughly) using a good compass based on magnetic north. I called the surveyor to ask some questions, but did not ask this question. They had indicated that this survey did not use GPS because "it was not used at the original time of the mapping". Rather it used metes and bounds. (The original development mapping was done about 40 years ago).
Is that unusual to use MAGNETIC north? Any help would be greatly appreciated.
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Depending on the survey, I'll still do it.?ÿ Out in the sticks, maybe don't even have cell service, there's no reason to bother about using something other than magnetic.?ÿ
If there's a plan of the abutter's lot, I may tie in and use that bearing system.?ÿ If not, there's nothing wrong with taking a few compass readings and using that.?ÿ It's the monuments that rule, anyhow, not the bearings
Oftentimes, a survey might be oriented to match the north orientation of an earlier nearby survey,
Agreed, that's most likely what happened here. Astronomic north (determined by sun or star observations) was also a common basis of bearings, and if declination is/was not too substantial in your area, magnetic will be pretty close to astronomic.
Magnetic North would indicate that the survey was based on the magnetic needle of a compass.?ÿ Using a compass for orientation of a survey is unusual for today standards but allowable provided the compass is adjusted on a yearly basis.?ÿ The magnetic declination varies throughout the country and therefor the declination of the needle must be adjusted for the region you are working in.?ÿ A magnetic variation map of the country will provide you with the variation of your region and year in question.?ÿ Some areas of the country magnetic North and True North are the same.?ÿ Some areas the difference will be considerable.?ÿ?ÿ
Example:?ÿ About twenty years ago someone called me to run a property line that had been surveyed a few years prior.?ÿ The man's wife had inherited the property and he was sure the surveyor wrong and had taken some of his wife's property.?ÿ When I met with the landowner he explained that he had leased a transit with a compass and using the survey plat had run the line on his own and missed the surveyed corner by about fifty feet.?ÿ I politely, asked him what the declination on the compass was set for and all of a sudden, that deer in the headlights look came across his face.?ÿ The compass on the transit was set on zero declination.?ÿ After doing a quick calculation of the declination to the property line was just fine.?ÿ?ÿ
"In early court trials,... the courts usually chose direction as determined by the compass."
--Brown, et. al. "Boundary Control and Legal Principles," 3d ed., Sect. 3.8.
Magnetic is still in use hereabouts (central Maine), as a number of our colleagues have not yet acquired GPS and are resistant to doing so. If we're interpreting an old deed or survey map, the presumption is usually that it's based on Magnetic. There are occasional exceptions.
Years ago I was part of a crew that got called in to help a contractor find "true South" for a fancy solar water heating unit he was installing. He was aware that local declination was about 18 1/2?ø, and had therefore laid out the unit using a hand-held compass and had proceeded to pour concrete. But he had not understood that declination around here is WESTerly of true north, and thus, having thought it was easterly, had screwed up his layout by 37?ø, which was enough to matter for solar. He had to tear out the concrete and do it over. Cost him some money. Luckily he had screwed some friends of mine out of a bunch of money a year or two before that, so I got to laugh -- instant karma nailed him.
In the early days of our country the magnetic compass was the best instrument available to control the direction of lines. So a lot of lines where shown relative to magnetic bearings. As years go by, even with better methods available, re-surveys may be done on the same basis of bearings as the original ones being retraced. So a modern survey might be done on the basis of magnetic bearings,?ÿ even though there wasn't a magnetic compass anywhere in sight.?ÿ ?ÿ ?ÿ ?ÿ?ÿ
https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml#ushistoric
As we all know, declination changes over time. The link above provides historic declination data. Page indicates accuracy is 30 minutes. Sample output is shown here:
