Yes, why don't people spend their time doing the extra work to figure out the exact number of meaningful digits in their measurements when the defaults work just fine for their non-scientific, non-metrological purposes?
A mystery for the ages.
A mystery for the ages.
Imagine, for a moment, that someone uses these values to put up a fence. Is the fence on their property? Those crap values beyond the actual significant digits of the measurement may tell you that you are, when you're not. That will cost you time and money down the road.
They're like the physical-world equivalent of a URL; I don't honestly care if there's an unused query string parameter tacked onto the end of it or if it redirects to https or something; all I care about is that the link I clicked on gets me to the correct cat video.
The relationship between trailing non-zero digits in the decimal representation and trailing non-zero bits in the significand is not one-to-one.
One third in a trinary representation would be 0.1. In decimal, 0.33333333333...
Mostly fruitless overprocessing. Only time I'd consider doing this would be for an epic ASCII dump of coordinates.
The context is that it's in a database serving up business locations. How is the geographic area owned (or occupied?) by a business reduced to a point? They don't say, so it's clearly unreasonable to expect accuracy and precision beyond, say, property boundaries, and perhaps not even that.
It would be madness to infer that the extra digits denote precision beyond the crude bounds set by context.
It would be further madness to reverse engineer a property boundary -- an entire path of points -- from a single point in a database.
FWIW, the error margin for 6 significant digits is around 11 cm. Accurate enough to point at a computer mouse.
It doesn't.
If you want to argue that Google Maps could do more to highlight the accuracy/precision limitations of its projected imagery, I'd completely agree -- but that's a different argument.
You can easily try and overlay county parcel data into google earth and see how many features don’t align with the sat imagery.
That's why people get concerned about this; that's why posts like this are important.
In any serious application you should have known error values and probably be using a more appropriate projection. If you need to accurately locate something you need someone trained to do that with the right equipment.
Online maps aren't respecting this, they're giving decimeter precision values on maps that are lucky if they're accurate to within meters, if not tens of meters. That's the problem.
Are you working with plans that show decimal degrees at a specific precision? I am curious what domain that is.
That's not true nor is it the problem at all. The thesis was that the values, albeit correct, have too many significant digits, which in turn reflect differences which lie somewhere between having no practical use or being absurd.
> Imagine, for a moment, that someone uses these values to put up a fence.
That example is very poor. Any engineer can tell you that a measurement is meaningless without tolerances/margin of error, and the tolerance in effect when putting up a fence is not expressed in a microscopic scale.
Reporting a value with too many significant digits is the same as reporting an incorrect margin of error, which (arguably) makes the value wrong.
But these locations are very precise, indicating high accuracy/low margin of error, but they don't have that high accuracy. In fact, the error could be in meters, rather than in the implied millimeters, so it definitely could be a problem for a fence.
Here is a college textbook chapter detailing types of precision and accuracy errors in GIS systems: https://www.e-education.psu.edu/geog469/book/export/html/252
"GIS users are not always aware of the difficult problems caused by error, inaccuracy, and imprecision. They often fall prey to False Precision and False Accuracy, that is they report their findings to a level of precision or accuracy that is impossible to achieve with their source materials. If locations on a GIS coverage are only measured within a hundred feet of their true position, it makes no sense to report predicted locations in a solution to a tenth of a foot. That is, just because computers can store numeric figures down many decimal places does not mean that all those decimal places are "significant." It is important for GIS solutions to be reported honestly, and only to the level of accuracy and precision they can support."
Or in other words, don't build a fence relying on naked coordinates of high precision but unknown accuracy.
Even if the values were precise, the fence can never be precisely located. Land/parcel demarcations don't work that way. Also, GPS coordinates change over time. Or rather, the land underneath moves.
Fence or other land locations are always relative (to an official surveyor's point), not absolute.
Rewinding a little:
> Imagine, for a moment, that someone uses these values to put up a fence.
There's your first problem.
Using a useful tool to do something useless doesn't make the useless thing useful.
Sometimes significant digits are too primitive a tool for error communication, and you might have to use the parameters of a normal distribution, some other distribution, or even a histogram. Other times significant digits are too cumbersome because it would take time to discover the precision in a situation where nobody actually cares beyond a crude threshold. This is one of those other times.