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How is magnetic North depicted on a survey map?
Posted by landbaron28 on July 9, 2013 at 3:38 pmI’ve received a copy of a 1979 surveyors map for a 4 acre land parcel I’m considering purchasing. I’m mainly looking to see if I can locate the property corners when I plan a visit in the next few days.
On the map is what appears to be a stretched or elongated looking, one-sided arrow with a trailing line out the back sitting in the center of the (more or less square) property boundary map.
Can I assume this is the marking for magnetic north with the head end pointing towards compass north?
Can I then use this with a map compass and sports tape to try and locate the markings?
Seymore Bush replied 10 years, 8 months ago 11 Members · 15 Replies- 15 Replies
You cannot assume that. There should be some kind of reference as to what that north-arrow represents. It could say “magnetic north” or “astronomic north” or “assumed north” or something else. If you can’t find any notation on the map anywhere, you can’t really presume it to be a particular north. (It could point north and state what the magnetic declination is as well in which case you could have the north arrow and know how many degrees off that arrow mag. north is).
Study the map for some kind of notation as to what the basis of bearings are and if you see some kind of abbreviation you don’t understand, someone here would probably know what it means.
Thanks Tom.
All I find is the name of the parcel owner at that time, the seal of the surveyor, his signature, town’s received date stamp, a Mead ruler was layed down for scale but that may have done later on by someone at the town. It is a slightly smaller copy of the original “copy” the town had. I can see the original page edges so I assume everything that was there is there.
I also have the newer version of the entire area from the town and the small N_S E W compass stamp in the corner does not match the direction of North for this map when set next to each other. They are both “generally” North but not pointing close at all.
Any thoughts?
Call the original surveyor that signed the map… he should be able to give you some accurate info, the rest of us are just wild guessing.
Perhaps the original surveyor can go out and show you his markers for less cost than a motel room and dinner, worth asking!Ditto Peter. There may also be original notes somewhere. That original surveyor may have always determined his north the same way; but the fact is that it is unknown unless he noted his basis of bearings. If he shows points in the ground, a survey will typically find those points and then establish a bearing on that line to figure out the difference between his north and the original published north; but that doesn’t help when you haven’t found the points in the ground yet. What you need to accept is the fact that your search area will be relatively wide until you figure out what his north was based on.
Often times a survey map will have an arrow pointing north, and show the deflection to magnetic north. Maybe that has to do with the little compass drawing. There are places to look up what the typical magnetic declination is in your area. Magnetic needles are typically not very precise and tend to move around a lot or sometimes point toward local magnetic attractions pulling them off the ‘magnetic’ north as well.
If you want to know which way NORTH is, just look for the cows.
Which way are THEY facing? 😉
http://www.wisegeek.com/why-do-cows-face-north-south.htm
Geezer
Apparently the original surveyor is still in business. I called him and left a message. Hope he gets back to me and still have his maps stored some place.
>…..
> Can I assume this is the marking for magnetic north with the head end pointing towards compass north?
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> Can I then use this with a map compass and sports tape to try and locate the markings?First never assume anything. Since we don’t know what area of the county you are from it will be even more difficult to give a direct answer. Each locality has standards of practice that can change significantly.
Plus this survey was done in 1979. The standards of that time are different than today’s. If it were a private surveyor then it was likely based on a prior recorded surveys “Basis of Bearings”. It was a simpler way of determining North without having to actually survey it.
If you are just looking for the corners it will probably be close enough for a compass and whatever a sports tape is. But no guarantees. 😀
:good:
I know of an old firm here in Ak that used a graphic of an Eskimo using an atlatl to throw a spear at Polaris. The direction and size of the ‘spear tip’ showed showed the direction and degree of magnetic declination at the time of the survey.
I tried something cool like that years ago, and had it promptly rejected by the first borough platting authority that saw it. 😛
That is the biggest pile of bovine manure I have ever encountered. As you know, I spend a lot of time standing around with cows. They align with little else than the next bite of feed or sip of water. Alignment will depend much, much more on environmental factors like wind direction and position of the sun in the sky on cold days and hot days where certain alignments provide better comfort. BTW, I resent them nosey satelites monitoring my activity.
That can vary widely but here in California a lot survey of that vintage is most likely oriented to a record version of north which may be off a degree or two and is close to true north, not magnetic.
If it is rural then it is possibly oriented to true north based on observing the sun.
I use a declinated compass for recon purposes when the bearings on the map are true.
Multiple problems exist with your plans. First, as has been mentioned, north could be any one of several options such that a dime-store compass will give you more grief than you can imagine. Trying to accurately measure significant distances alone is time consuming and frequently not particularly accurate. Finding the survey monuments can be an entirely different frustration, even by experienced surveyors with good equipment. First comes the biggest collection of poison ivy you have ever seen, centered in your search area. Then comes the extraneous metallic objects that set the metal detector to singing much like the “Real McCoy”. Then you find a 3/4″ rebar about three inches from a 2″ diameter pipe sticking up a foot and, then, a car axle right next to that. If the survey says “I.P.”, it might be any of those things. I can’t tell you how many times I have found what must have been the “I.P.” close to a nice looking corner post and eventually discover the “I.P.” has been moved so the nice looking corner post could be placed very, very close to where it was originally placed by the surveyor.
Also, your walk-around of the property will not reveal all sorts of potential issues with the property and adjoiners and their rights.
There are times when being a do-it-yourselfer is a good thing. Other times it can be very expensive in the long run.
An example: A fellow comes to me to slice off a piece of ground he wants to buy to put a really neat cabin on. He likes to socialize on weekends with lots of friends. He has convinced the current owner of the parent tract to sell him this two-acre piece of Paradise. I meet him on-site and start shaking my head immediately. I ask him if he has talked with the local rural water district about getting a water service line to this location. No, of course. I explain that I happen to know the nearest line is over 3/4 mile away, through almost 100 percent bedrock. That alone will run somewhere between $10,000 and $15,000 plus the cost of purchasing a benefit unit. What’s a benefit unit, he asks. That’s the one-time fee you must pay to have the right to connect to the RWD. That’s another $1000 or more. Then I ask, what are you going to do for your septic. He says, put in a septic tank, I guess. Sir, this property only has about four inches of soil on top of rock that reaches to China, there is zero potential for a standard septic system. You will almost definitely need to pump your sewage into an above ground storage tank and have it pumped monthly or more often depending on how many friends you have and how much water they use. Oh, did you happen to notice there is no power line for over one-half mile from here? I’d advise you to have a chat with the power company to find out how many thousands they are going to charge you to extend the line to this site. And, by the way, I’m betting the owner told you this property reaches all the way over to that county road over there. Well, it doesn’t. See that little bit of ancient barbwire fence that has nearly collapsed. This land starts about 30 feet this side of that old fence, not the extra 300 feet over to the road. Did you notice how that road is built across the top of a lake dam and it’s spillway? There’ll be about 10 days per year you can’t get across the spillway due to heavy rain. Oh, by the way, I will need to do a full section breakdown to find two of the four sides of this tract you plan to buy, so I won’t be in and out of here in less than 2 hours for under the $100 you were thinking about.
Way back when, shortly after they invented maps, I was a cartographic drafter in the Army. It sounds like your surveyor is using the symbols that the Army used on its maps.
On a standard topo sheet there are 3 Norths. Grid North (a line with “GN” above it, True North (a line with a star above it) and Magnetic North (the referenced “half arrow” symbol). Evidently he is using that arrow symbol to indicate Magnetic North. There also should be a listed differance between Grid North and Magnetic North. This is the used “magnetic declination” for that date and time.
In the old days, surveyors used isogonic charts to determine magnetic declination and the Army Map Service also published declination diagrams for each area. This may explain the diferance between the declination of the two surveys. Surveys done at different times could easily have different declinations.WOW! Now I need to try that!
Basis of Bearings: Taken off a herd of cows, on 6/4/2013
I wonder what the state land surveyors office would think?
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WOW! Now I need to try that!
>>I wonder what the state land surveyors office would think?
Up here they’d make you use moss on tree trunks if something precludes the more rigorous seasonal observation of birds.
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