I have a 1987 survey of land we acquired. Bearings are stated as magnetic. We will be visiting the plot this week and trying to roughly determine what's on the land from the bearing on the survey from the irons. The declination table is below for the location from 1987 to 2023. As the survey bearings are not true north and are magnetic, am I right to adjust my bearings 3 degrees E and will then have a rough boundary line. For example, the bearing from one pin is 57.2 degrees and now would I follow a 60.2 degree line?
Apologies if this is the wrong forum for this. We have plans for a proper survey and blazing, but we'll be in the area this week and just want to know what we are getting into 🙂 Many thanks in advance and I appreciate your input
# Magnetic Model: USD80 before 1985 and IGRF thereafter
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Year Coordinates Declination
1987 45.27986 -69.26475 -18.48
1990 45.27986 -69.26475 -18.43
1995 45.27986 -69.26475 -18.32
2000 45.27986 -69.26475 -17.97
2005 45.27986 -69.26475 -17.45
2010 45.27986 -69.26475 -16.95
2015 45.27986 -69.26475 -16.43
2020 45.27986 -69.26475 -15.85
2023 45.27986 -69.26475 -15.48
My best advice to you is not to attempt this yourself using a compass. A 1987 survey would not even be based on magnetic bearings unless antique equipment with a drop needle compass onboard were used.
You mentioned having the lines blazed, If I were you I would hold off until that happens so you can see what you are really getting into. You likely will not be able to walk a straight line with a compass in the woods without meandering around obstacles and being able to stay on the desired line. There also could be other situations that would attract your compass needle and give you false readings.
In Maine if your magnetic compass reads 27deg azimuth or 27 degrees NE then the true azimuth or bearing is 45.8 deg or 45.8 deg NE in 1987. Today if the magnetic compass reads 27 degrees then the true azimuth is 42.8 deg.
If you want to try and walk the 1987 magnetic bearings you will need to read 3 degrees more than what they read in 1987.
Yes, you were correct in your conclusion.
Thanks, I appreciate the input. I have included a snippet from the notes of the survey below where it states "SOURCE OF BEARINGS: Magnetic as derived from the south line between..." . Am I right in assuming then that they truly just did this survey based off of magnetic north? Thanks again
The note you posted is incomplete. I'd bet that the surveyor tied to a line from a previous survey and no magnetic bearing was directly observed.
In my area (Athens, Ga), most record plats have a north arrow that calls for magnetic north but I'd venture to guess that not many in the past twenty years were directly observed with a compass.
If you have a short line on your survey that you could observe and compare, that might help you in reconnaissance.
Thanks for the reply. Does this help? Here is the more of the Note on survey re: Bearings.
The survey refers to an older instrument as a basis. It's doubtful that a surveyor in 1987 did anything magnetic. All he is saying is that the 1987 survey was based on an earlier adjoining survey which was based on magnetic bearings.
Probably this cascades down from many years ago and many surveys.
@alowell Yes. Based on that note, my best guess is that he used that line and accepted the bearing from the 1968 plat. If magnetic north was directly observed in 1968, that's where you would want to get your declination from.
If all you are doing is trying to get a rough idea of the lay of the land, I don't think you will have to worry too much about the declination. As someone said above, it will be quite difficult to follow a compass bearing through the woods. How large is the property? Are we talking 5 acres, 50 acres, or 500 acres?
My best advice to you is not to attempt this yourself using a compass. A 1987 survey would not even be based on magnetic bearings unless antique equipment with a drop needle compass onboard were used.
You mentioned having the lines blazed, If I were you I would hold off until that happens so you can see what you are really getting into. You likely will not be able to walk a straight line with a compass in the woods without meandering around obstacles and being able to stay on the desired line. There also could be other situations that would attract your compass needle and give you false readings.
This is not necessarily true. In 1987 we had a compass attachment for our total station, and often turned an angle from a traverse line to magnetic north, so the office could orient our work to magnetic north, if they so wished.
That said, I agree that a layperson without experience should not run a compass line through the brushy woods of Maine, especially if your line is longer than 200'. It's very easy to get off course, especially if there are any large rocks with iron in them near your compass, or deposits in the bedrock. Such "local magnetic attractions" abound in the northeast.
alowell, by any chance is your lot long and narrow, something like 200' wide by 1,500' long? Patten Corporation was infamous for creating and selling lots like that in Maine around that time frame.
Thanks all. So just looked up that 1968 plat and only found a few things. The indication of mag north and the "south line" that is referenced. No notes 🙂 Shown below.
Sorry, forgot to answer the other questions here. Yes, this lot is about 15 acres and about 300' wide on one end and 200' wide on the other end, it's narrow
Sorry, forgot to answer the other questions here. Yes, this lot is about 15 acres and about 300' wide on one end and 200' wide on the other end, it's narrow
I used to run lines in the Maine woods with a compass that could be read to 1/2 degree of bearing (made by Silva). Over 1500'+/- of line I would usually be 30 to 80 feet off my target by the end, occasionally more, never less. That was hanging flags every 20-40 feet with an assistant eyeballing the back line of flags to maintain a straight line. I doubt that without training you will be that close if you try to run them yourself. You would do well to wait for your surveyor to mark the lines.
