I have a survey plat made in 1915. The description is written in bearings and distances but in the notes section there is a remark - declination 0 deg 20'.
So do I rotate the bearings by 20' clockwise? counterclockwise? or do I use the bearings as is?
> I have a survey plat made in 1915. The description is written in bearings and distances but in the notes section there is a remark - declination 0 deg 20'.
> So do I rotate the bearings by 20' clockwise? counterclockwise? or do I use the bearings as is?
I believe they are telling you what to set the declanation at, on your compass; but I'm not from the Netherlands....
That would be what the declination was at that location in 1915. The reported bearings are magnetic. You would apply the declination reported for that time to the magnetic bearings to get true north. Then you would figure out what the declination is in that same location today, apply that to the true north previously calculated to figure out what bearing you would run with your compass today. That is a common situation here in West Virginia.
".. figure out what bearing you would run with your compass today. That is a common situation here in West Virginia."
Am i reading that correctly? Even if you were trying to follow the original footsteps, it would seem the conditions have changed through the years.
Uh, that's why you make the adjustment he outlined, IF you are going to run with a compass. The only relevant values are what they were on the original date and what they are today. The declination changes over the years in between readings have no bearing on the issue. (Pun intended, no matter how lame it may be. :-$ )
> I have a survey plat made in 1915. The description is written in bearings and distances but in the notes section there is a remark - declination 0 deg 20'.
> So do I rotate the bearings by 20' clockwise? counterclockwise? or do I use the bearings as is?
My first supposition would be that the survey was made under the assumption that magnetic North had a geodetic azimuth of 0°20'. I'm assuming that this plat covers a locality where that declination would have been reasonable in 1915. If not. some other explanation is probably in order.
To use that information, you must have an estimate of what the declination actually probably was in that locality in 1915. From that, you can correct the bearings shown on the plat to either true or to some mapping grid.
The other bit of useful information that the plat contains goes to methods used in the survey. If the bearings are expressed to a precision consistent with what one might expect from a reading of the sort of compass used by surveyors in that locality ca. 1915, then ordinarily I'd assume that the plat depicts a compass survey, not one made with a transit or theodolite, and I would have different expectations of the accuracy attached to the bearings noted on it.
I agree.
It all comes down to footsteps. Finding the first footstep. Then the next step. I'm working on one now that has a 43 minute declination to geodetic north. The bad of it is it's not a compass bearing. At least I don't think so? 1993. Any way, once I found the first 2 steps, I rotated my model to geodetic north. Now I can find all the steps. And have. But that's just basic surveying. The good and the bad. Or turning the bad into good.
One more thing. I have found others could measure distances fairly well.
It appears the direction of the declination may not have been given and cannot be assumed. If that is the case then perhaps you could visit the National Geodetic Survey (NGS) Website (currently shutdown) and see if you can use the "magnetic declination calculator" tool. I have never verified if the tool works internationally, but I don't see why it wouldn't. This might give you some evidence as to the direction and also verify the value of the declination as well.
Otherwise, one might temporarily eschew the preliminary calculations and set out to discern the intended direction by identifying and observing the most easily retraceable and apparent boundary(s) in the field. The correct direction of the declination and a reasonable assessment of the required rotation may be surmised that way.
Thanks for clearing that up CD. I was just surprised that a surveyor would go to those lengths to re-create the original footsteps. I was thinking that some of these compass surveys could be quite old, and wondering to myself, what other conditions might have changed over these many years.
Not Enough Information
Search records, military or university for historic declinations. You need 1915 and 2013, however records are most likely 1910, 1920, 2010 etc.
Also look for words in the deeds such as "as the needle ran" to confirm that the deed is compass readings and not adjusted compass readings.
Adjust the deed to true, then adjust to current decilination. Or adjust the deed to true and adjust your compass to current declinations.
"Following the footsteps" means you use the previous surveyors methods, compass readings, rather than exactly equivalent values. Finding original monuments can confirm the declination.
Since the original surveyor did not have the internet to research declination how did he know what it was? It is most likely he used a pair of true North monuments set in the park in front of the local county courthouse. You may still be able to do likewise.
Paul in PA
Not Enough Information
> Search records, military or university for historic declinations. You need 1915 and 2013, however records are most likely 1910, 1920, 2010 etc.
>
> Also look for words in the deeds such as "as the needle ran" to confirm that the deed is compass readings and not adjusted compass readings.
> Since the original surveyor did not have the internet to research declination how did he know what it was? It is most likely he used a pair of true North monuments set in the park in front of the local county courthouse. You may still be able to do likewise.
Do we suppose that there is such a thing as a "local county courthouse" in the Netherlands? "As the needle ran" doesn't sound like Dutch to me, but I suppose it could have happened.
> I have a survey plat made in 1915. The description is written in bearings and distances but in the notes section there is a remark - declination 0 deg 20'.
> So do I rotate the bearings by 20' clockwise? counterclockwise? or do I use the bearings as is?
I believe you may be able to approximate your current magnetic declination at this web site "Find the magnetic declination in Netherlands" and learn more about the subject at "Natural Resources Canada, Magnetic declination" or Wikipedia.
Also as noted by others the direction of declination in 1915 is important. The normal notation is positive east (clockwise) and negative (counterclockwise) west. When working with bearings this can exceed the 90° limit of the bearing quadrant and make computation of current (2013) bearings more confusing. magnetic north is in constant motion that is monitored by geodetic scientists. This subject matter has consistently been one of the more difficult things for surveying students to grasp.
Nord, Zuid, Oost and West
Commonly declination is + East and - West.
Compass calibration is provided by marine suppliers in the Netherlands.
The Netherlands has 12 Provinces but I cannot confirm if deeds are recorded in provinial or local records.
Paul in PA
>magnetic north is in constant motion that is monitored by geodetic scientists. This subject matter has consistently been one of the more difficult things for surveying students to grasp.
To my mind, the simplest way to present is it so say that magnetic North has a particular geodetic azimuth (subject, of course, to daily variation and magnetic disturbances).
The bearings of a historical survey are also converted to azimuths and the process of comparison then becomes simply one of adding or subtracting a constant to convert or compare without needing to pay attention to quadrants and signs.
>
> To my mind, the simplest way to present is it so say that magnetic North has a particular geodetic azimuth (subject, of course, to daily variation and magnetic disturbances).
>
> The bearings of a historical survey are also converted to azimuths and the process of comparison then becomes simply one of adding or subtracting a constant to convert or compare without needing to pay attention to quadrants and signs.
Kent I agree. However, the problem usually is accepting that magnetic north moves! The next difficulty is the correct application of + or - declination to get the correct constant. If the historic and current are different signs most will add when subtraction is required or the opposite.
Next once the correct constant is know many will apply it with the wrong sign. Usually takes about 30 minutes to convince students that a sketch is required to understand the problem and apply the correct steps. Most want to just grind numbers without taking the time to visualize the situation.
Looks difficult to know whether the old surveyor meant +20 minutes or -20 minutes.
It's easy in my area because declination is around 15.5 to 16 degrees so there is no confusion whether it's positive or negative.
But only 20 minutes off from true north should be close enough to find the physical evidence and you can put your own favorite brand of North on the survey!
I work under the assumption that the bearings in the deed are as close to geodetic as possible after the scriveners application of the declination they provide as being that which they used to get from mag to true.
With tools today, one can estimate the historical declination of the area and, if it's wildly different than what was used in the deed, then that helps aid in retracing the lines and helps to give an expected bearing along the line.
Many times we have deeds from the mid 1800's that are 8 to 10 degrees. The lines on the ground are pretty close to North or whatever the bearing is supposed to be. In the 60's it was around 6 degrees East here, and now it's very close to 3 degrees East.
Scriveners Never Adjusted Anything.
They were sworn to copy it as it came.
Paul in PA
Scriveners Never Adjusted Anything.
Thank you for the replies. The plat says grid so the magnetic bearings were converted to grid by adding or subtracting the declination amount. So if this was done then why need to mention the declination in the plat? Itwas another fact that confuses future surveyors. Or maybe it is only me that was confuse.