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I've sometimes wondered how surveyors deal with a similar, but more extreme situation. Many properties, at least in the northeastern United States, are defined

I've sometimes wondered how surveyors deal with a similar, but more extreme situation. Many properties, at least in the northeastern United States, are defined by "metes and bounds". A combination of landmarks, distances, and compass bearings. Newer properties metes and bounds are often based on the older metes and bounds as an old farm is split up, and can be hundreds of years old. But magnetic North moves by dozens of miles each year, and has shifted from Russia to Canada and back, moving by hundreds of miles. The closer you are to the poles the more inaccurate compass readings will become. Based on the alignment of old stone walls[0], they think over the last few hundred years magnetic north has drifted by around 7 degrees in the northeast US, should be worse in England. When the property description uses a bound of a road, a stream, or other landmark, then the rest is all based on compass readings and distances of up to miles, that can make a huge difference. I believe finding that your house is on your neighbors property is solved by "adverse possession" laws (sometimes referred to as squatters rights?) where if you act like you own something, and everyone else acts the same way for long enough time, it doesn't matter what the land records say, that is your property. It's a way of cleaning up mistakes. Oddly, since GPS values will necessarily shift as the Earth's surface moves around, I think the old metes and bounds can be more accurate over time as long as it is based on true North instead of magnetic North. [0] http://theconversation.com/old-stone-walls-record-the-changing-location-of-magnetic-north-112827 http://theconversation.com/old-stone-walls-record-the-changi...

ajross 7y ago
Even if the surveying continues to be both local and continuously observed, and the shapes of properties are changing over time, the current system works just fine. Properties change, and their values change, and owners adapt. Really this is no different in a practical sense than having a house on an eroding beach, or (sigh...) in a sinking city.
epc 7y ago
I think I have a property defined like that (in Rhinebeck, NY). The deed is based on static landmarks, the only directional mention is from stone landmark to landmark (ie, walk North 120 feet to a landmark set 4 feet from Paper Street). No reliance on magnetic north. Allegedly when the village was laid out they sunk stone landmarks at the intersections of the original properties.
mgsouth 7y ago
I'm not a surveyor, but was the IT guy & supervisor for a city's two-engineer surveying team as we went GIS... Basically you fudge it. Precision losses, errors, and local ground movements swamp continental drift. As you noted, some of the original sources go back over 100 years. A huge, huge amount of the surveyor's time was spent cleaning up data. One of the steps was to map the vectors around a plat. There was always some kind of closure error when you get back to the beginning position. The surveyor's job was to tweak the points to resolve the error. Kind of like auto body work; he used a lot of skill and experience in making the most seamless repair possible. (The most important part of my job was running interference for him, nobody understood why it took so long to "just digitize some maps".) In general the original surveying records remain the source of truth, and the maps we produced with the tweaked coordinates were working documents. To be technically correct, another map would have to go back to the original documents and re-apply corrections. IIRC for some really egregious problems there were ways for the surveyor to amend the official truth. Automating or re-implementing legacy systems is always a horribly messy data-cleansing exercise, but I think this was the most mind-numbing, tedious, endless slog I've ever been involved with.
beerandt 7y ago
Short answer, surveyors don't use absolute coordinates, only relative ones from locally known points, output as distance and bearing. The actual coordinates "cancel out" of differential GPS, which also makes it much more accurate (and precise) than standalone GPS. Differential GPS (and newer VRS) gets sub-centimeter horizontal accuracy, and has been available for over 20 years. Same goes for North. You try to get it close, but it's the relative angles between bearings that actually matter. So it doesn't matter if magnetic North changes or if there was an error initially measuring it. For legal descriptions of boundary surveys, "what's on the ground" is what controls. Meaning an iron pipe set as a corner doesn't "mark" a property corner, but defines it (unless it's an offset, but it's still the defining feature). The legal description is more a treasure map than some idealized abstract legal "truth". This especially applies to metes and bounds. GPS coordinates are generally not used for boundary surveys, except maybe to drive to the job site. As for neighbors: the only people who can decide where a property boundary falls are the adjoining land owners. It's sort of zen, but the boundary is whatever you agree it is. It fits with the "local first" philosophy. In the absence of agreement, prescriptive acquisition (or judicial delineation) is the general term for when the courts have to become involved in a dispute (because the judge prescribes). "Adverse possession" is a type of positive defense to claim prescriptive acquisition when the party has no good-faith claim to the title. It's what most people think of as squatter's rights. Philosophically, it's not for cleaning up mistakes, but returning idle or abandoned real estate back into active commerce. "Good-faith possession" is if you think you have a legal claim to the property, like if you bought a bad title, or a property owner sold the same lot twice, and has a much lower burden of proof and required period of possession (generally ~30yrs adverse vs ~10yrs good-faith) Judicial delineation is more for bad boundary descriptions or cleaning up mistakes, but there's no need for judges if the neighbors can come to an agreement on their own. They just have to file an amended plat with the conveyances at the courthouse.

ajross 7y ago

Even if the surveying continues to be both local and continuously observed, and the shapes of properties are changing over time, the current system works just fine. Properties change, and their values change, and owners adapt. Really this is no different in a practical sense than having a house on an eroding beach, or (sigh...) in a sinking city.

epc 7y ago

I think I have a property defined like that (in Rhinebeck, NY). The deed is based on static landmarks, the only directional mention is from stone landmark to landmark (ie, walk North 120 feet to a landmark set 4 feet from Paper Street). No reliance on magnetic north. Allegedly when the village was laid out they sunk stone landmarks at the intersections of the original properties.

mgsouth 7y ago

I'm not a surveyor, but was the IT guy & supervisor for a city's two-engineer surveying team as we went GIS... Basically you fudge it. Precision losses, errors, and local ground movements swamp continental drift. As you noted, some of the original sources go back over 100 years. A huge, huge amount of the surveyor's time was spent cleaning up data. One of the steps was to map the vectors around a plat. There was always some kind of closure error when you get back to the beginning position. The surveyor's job was to tweak the points to resolve the error. Kind of like auto body work; he used a lot of skill and experience in making the most seamless repair possible. (The most important part of my job was running interference for him, nobody understood why it took so long to "just digitize some maps".) In general the original surveying records remain the source of truth, and the maps we produced with the tweaked coordinates were working documents. To be technically correct, another map would have to go back to the original documents and re-apply corrections. IIRC for some really egregious problems there were ways for the surveyor to amend the official truth. Automating or re-implementing legacy systems is always a horribly messy data-cleansing exercise, but I think this was the most mind-numbing, tedious, endless slog I've ever been involved with.

beerandt 7y ago

Short answer, surveyors don't use absolute coordinates, only relative ones from locally known points, output as distance and bearing. The actual coordinates "cancel out" of differential GPS, which also makes it much more accurate (and precise) than standalone GPS. Differential GPS (and newer VRS) gets sub-centimeter horizontal accuracy, and has been available for over 20 years. Same goes for North. You try to get it close, but it's the relative angles between bearings that actually matter. So it doesn't matter if magnetic North changes or if there was an error initially measuring it. For legal descriptions of boundary surveys, "what's on the ground" is what controls. Meaning an iron pipe set as a corner doesn't "mark" a property corner, but defines it (unless it's an offset, but it's still the defining feature). The legal description is more a treasure map than some idealized abstract legal "truth". This especially applies to metes and bounds. GPS coordinates are generally not used for boundary surveys, except maybe to drive to the job site. As for neighbors: the only people who can decide where a property boundary falls are the adjoining land owners. It's sort of zen, but the boundary is whatever you agree it is. It fits with the "local first" philosophy. In the absence of agreement, prescriptive acquisition (or judicial delineation) is the general term for when the courts have to become involved in a dispute (because the judge prescribes). "Adverse possession" is a type of positive defense to claim prescriptive acquisition when the party has no good-faith claim to the title. It's what most people think of as squatter's rights. Philosophically, it's not for cleaning up mistakes, but returning idle or abandoned real estate back into active commerce. "Good-faith possession" is if you think you have a legal claim to the property, like if you bought a bad title, or a property owner sold the same lot twice, and has a much lower burden of proof and required period of possession (generally ~30yrs adverse vs ~10yrs good-faith) Judicial delineation is more for bad boundary descriptions or cleaning up mistakes, but there's no need for judges if the neighbors can come to an agreement on their own. They just have to file an amended plat with the conveyances at the courthouse.