Magnetic Bearings / Sanborn Maps

I have only every seen a Sanborn map in a museum and was struck with how concise it was.

https://en.wikipedia.org/wiki/Sanborn_Maps

http://www.davidrumsey.com/blog/2011/6/27/pre-earthquake-san-francisco-1905-sanborn-insurance-atlas

Magnetic Bearings and declination were know by surveyors long before that description was created. Typically if Magnetic Bearings were cited the Declination correction was used... hence Magnetic Bearings = True Bearings to the extent of the technology of the day, and the capabilities of the Surveyor. Correct for the change in Declination to "follow the footsteps".
Two possibilities:
1. Perhaps the actual description was created by a Non Surveyor and the data was complied using mixed sources (or parroting the words of others without understanding the terms.
2. Or the bank has moved... and that would lead to another discussion 🙂

Peter Ehlert, post: 348955, member: 60 wrote: Magnetic Bearings and declination were know by surveyors long before that description was created. Typically if Magnetic Bearings were cited the Declination correction was used... hence Magnetic Bearings = True Bearings to the extent of the technology of the day, and the capabilities of the Surveyor. Correct for the change in Declination to "follow the footsteps".
Two possibilities:
1. Perhaps the actual description was created by a Non Surveyor and the data was complied using mixed sources (or parroting the words of others without understanding the terms.
2. Or the bank has moved... and that would lead to another discussion :-)[/QUOTE

Peter,

It appears my question wasn't clear. The deed cited that the bearings were true, and it also cited the magnetic declination at the time. So that, along with the bearings being cited to the 1/4 degree, suggests strongly to me a compass was used, magnetic bearings were determined, and the stated declination was used to transform them into true bearings. I'm wondering about the likelihood of neglecting to transform the bearing of the first course ( and therefore it would still have been stated as a magnetic bearing in the deed) while all the rest of the courses were stated as true. I'm figuring this would be more likely if the compass didn't have a declination screw (or something of that nature) so that the compass wouldn't read a true bearing directly, like my Silva compass that reads true bearings directly as I already have the declination set in it. The surveyor would have to mathematically change all his/her field recorded bearings (or at least make a transformation in their head), and could have much more likely failed to do so on one of the courses.

By comparing Sanborn maps from 1883 through 1941, the bank was never in a configuration that supports the first course and its relation to the rest of the courses along the bank.

It would be nice to find more documentation (like a Map of the survey, or adjoiners description) that would clarify... but I suppose you have exhausted that search.
The decision I see for you to make is "is the boundary the Bank of of Thompson Creek" as the superior call (monument) or do you follow the math....

Yes, surveyors are fallible (excluding me). I would bet that the declination was properly dilled into the compass... all of the old ones I have seen had that feature.
More likely the writer parroted a phrase or two without understanding.

Peter pretty much covered the Magnetic/True Bearing question, so I'll stay out of that one.

As far as Sanborn Maps go, here's my 2 bits...

YES (I have used them when available, and germane to the issue at hand). A GREAT resource in many cases when dealing with some of the "Ghost Towns" here in the Great Basin (and some existent towns/cities as well). There is (or was) an Internet source for Sanborn Maps, but I haven't used it in 5 years or so, and don't remember how I found it).

I am not aware of any court cases dealing with the use (or MISuse) of Sanborn Maps in the analysis/determination of Boundary issues. BUT, I am unaware of a LOT of things!

John Stahl may have some information on that issue.

Loyal

the Second Tank

In the fall of 1990, during construction, the second tank was discovered and removed by Hospice. This second tank had not been reflected on any maps previously given by County to Hospice.

Sometime during 1991, Mr. Dan Johnson (an employee of an environmental consulting firm which had previously done work for Hospice) was working on an unrelated project and examining a packet of maps prepared in 1921 by the Sanborn Map Company. He noticed there was a map of the property depicting an underground storage tank adjacent to the kitchen of the old hospital. He reported his discovery to Hospice.

Some evidence existed to suggest this 1921 Sanborn map derived its information about the presence and location of the second tank from maps on file with County prior to 1921. Mr. William Ring, a County map expert, indicated the 1921 Sanborn map could have been based on or derived from County maps, but that the Sanborn map was not itself a county map. He further indicated he had personally searched County records and had not located any maps showing this underground feature.

-San Diego Hospice v. County of San Diego, 31 Cal. App. 4th 1048 (1995)

Peter Ehlert, post: 348958, member: 60 wrote:
The decision I see for you to make is "is the boundary the Bank of of Thompson Creek" as the superior call (monument) or do you follow the math

Well the natural boundary is definitely the superior call in most cases.

However, what do you then do? Just put new courses and distances along the bank today? Or just show the deeded lines, the location of the bank, and put a note that the deed calls for the boundary to be the bank?

I usually do the second option.

I am actually looking at the math as further extrinsic evidence to the location of the creek. The creek in this area does not exist anymore. It was replaced by a concrete culvert ( a "tube") during the Depression by a WPA project. The evidence for the creek location is the storm drain itself (presumably it was placed in the bed of the creek), the creeks approximate location determined by 1883-1941 Sanborn maps (scaling to still existing old buildings), and the "westerly bank" courses in the deeds. The courses substantiate the approx. location per the Sanborn maps when the above-mentioned first course is assumed to be mistakenly stated as a magnetic bearing and is transformed into a true one. I'm just querying what others thought about the probabillity of this "transposition" occurring in a compass and chain survey in 1900 or so.

More info, more ideas...
This is now sounding like the description is from an easement grant, and you are struggling with the owner of the easement. Not that it would change things...
I know nothing about Sanborn maps, but they could be complied from the same data you have in hand.

More info, more ideas...

Thanks for the links.

Sanborn's are pretty standard reference sources for folks doing Phase I Environmental Site Assessments.

They were used to evaluate Fire Insurance risks back in the day.

Like railroad valuation maps, I wouldn't give them the highest order of survey evidence, but they're still evidence, and in the absence of anything else, or to back up other evidence, I'd still definitely consider them if I had reasonable access to them. I wouldn't spend a fortune to get one, however.

There are internet sources for these, usually it's a license they have obtained to copy and distribute. It's a pricey service, but for the folks doing a lot of ESA's maybe sometimes it pays to subscribe. Here in Springfield, we have the State Archives and Library and have free and and easy access to many of them. We have to personally go get them, they won't send them to us (again a licensing issue). It's like the courthouse, it's easier if you to live close to it