We discussed a lot about land surveying in our blog but there are some fundamental that we’ve not covered before the measurement a land surveyor does. We’ll cover precision, accuracy, and errors.
What is measurement?
It’s important to go into detail about what “measurement” means to explain it more fully. There is only one true distance between two points on a flat surface. Likewise, there is only one acute angle that forms when taking two lines or rays. The act of determining these measurements is called measurement. Sadly, even the most accurate measurements are estimates aren’t perfect and have some margin for error. All measurements are still estimates!
Measuring is not the same as counting. Counting depends on indivisible fundamental units things or objects that can’t be divided any further. The smallest unit of money is the penny. You can’t count pennies, but you can measure them, or know how many there are without counting them one by one. If we take a £1 and change it to 50 pence, then we’ve changed the quantity without actually measuring it.
A geodetic surveyor’s job is crucial to the maintenance of real property boundaries. Geodesic measurements are only able to reflect a property’s current state, and they don’t take into account any past changes that may have occurred.
Boundaries are defined by the location of your property’s corners. Our measurements must be accurate in order to effectively establish boundaries, so we need to know what angle and distance relates to your corner of land. We’ll explore the procedures and history of boundary-related measurements, but just remember that while precise measurements are really important for boundary documentation, they don’t define boundaries themselves – boundaries are defined by you!
Precision vs Accuracy
“Precision” refers to the procedure used to arrive at a particular value or figure. Such as 0.0000 (4 points of precision). “Accuracy,” on the other hand, refers to how close the measured value is to the “true” value. Accuracy and precision are generally not used interchangeably when referring to dimensions measured with precision instruments.
For example, two men may be requested to determine the distance between two points. Person A looked at the two points and without any tools stated that the distance is 100metres.
Person B then uses a measuring tape and measures the two points a couple of time and determines that the distance is 100.05metres.
Person A’s statement is Accurate, and Person B’s determination is precise.
Measurement data can be presented in different ways (units such as metres, cm, inches, etc…), and the form of presentation can tell you about the precision of the measurements. This is a hint about how precise the measurements are, but it’s not foolproof. Sometimes people who report measurements without understanding exactly what they mean will say something that changes the implied precision.
The precision implied by a metric is often analyzed based on the way that it’s implied. A distance given in metres can imply much more precision than one given in miles. Likewise, a directional metric such as “directions” might imply less precision than one using degrees of the compass.
Dimensions are usually measured in units, with a single unit being the smallest possible measure. 22 feet, for instance, means that a foot is the smallest unit of measure and that there can’t be anything less than one foot.
if measurements were reported as the nearest inch, then distances from just over 21 feet, 111/2 inches to just under 22 feet, 01/2 inches would be reported as being 22 feet, 0 inches. The implied precision is such that these two measurements are considered different.
In addition to the four types of numbers, fractions also have implied precision. “One half of 1 foot” is not the same as “6 inches,” nor is either one the same as “0.50 feet.” The implied precision of 1/2 foot, for instance, is that there are smallest unit of measure was 1/2 of a foot; the implied precision of 6 inches is that there are smallest unit of measure was one inch; and the implied precision of 0.50 feet is that there are smallest unit of measure was one-hundredth of a foot. One-fourth mile isn’t equal to 15 minutes (and 1 acre isn’t 43,560 square feet) when we’re considering plausibility! Many a real estate maven has multiplied an area given in acres by 43,560 (square feet in an acre) to arrive at a square footage – which would make their sale predictions inaccurate by 21,780 square feet either way!
Measuring typically depends on the comparison of the thing you’re measuring to a standard or known value. Variations in accuracy, precision, and other factors can change the way you measure. These variables are called “errors.” If a Land Surveyor or scientist says that they had an error, they mean something different than it does if someone who doesn’t know how to measure said it. Errors are reduced by training, attention to detail, quality instrumentation, and a well- thought-out course of action.
There are three general categories of errors: systematic, random, and blunders. Systematic errors occur when you press a touche in reverse order. Random errors occur when devices give inconsistent feedbacks. Blunders are errors that occur because you pressed a touch early or late.
Systematic errors can be recorded inaccurately every time that a measurement takes place, which is an oversight in the system. For example, if you were to measure with a ruler that’s short by a small fraction, then all measurements would end up being inaccurate. You would mistake objects as being larger than they really are.
Random measurement inaccuracies occur when there are systematic errors in how much one side of a piece of wood is aligned with the other, or how the end of a ruler gets lined up with one side, for example. These errors are not the same each time you measure something and can’t be predicted because they tend to offset each other out.
Blunders come about when a measurement has been misinterpreted. For instance, someone might not be measuring carefully and mark the cut line 4 feet upwards. These mistakes can happen for many reasons and will typically involve two things that were intended—but in a different way. In the saying “measure twice and cut once”, it is an old saying that reflects the same idea of blunders—to work on your measure and act more carefully.
Blunders are random and extremely large. They most often cause conflicts, confusion, and economic loss in the survey profession. One way to reduce the risk of blunders is to employ rigorous measurement procedures.
All measurements have errors
Errors exist in all measurements, even precise ones. Imagine the following experiment. A classroom of high school students was instructed to attempt to measure with a ruler the dimensions of a teacher’s desk. The teacher requested that each student measure each dimension to the smallest fraction of an cm that he or she could estimate. As one would reasonably expect, some variations in the reported dimensions for the desk were submitted.
For example, the width of the desk might have ranged from 100cm to 105cm. If the average reported measurement was 102.5cm, then that means that there would be no error in the measurement of
+/- 2.5cm. The actual width of the desk would never be known.
The distance from the first molecule of desk on one end to the last molecule of desk at the other end is so small, it can’t be precisely measured. A school ruler isn’t calibrated, and the length of the ruler and the width of the desk are both likely to change with humidity and temperature (depending on the material). The different people doing measurements will also affect how they measure things. The difference between what you see as an absolute measurement and what others see as a reported average is much wider than our measurement error suggests.
The students could measure the end to end while recording the humidity, temperature, and other factors for each reading to keep it constant and work out a more accurate. But even if you used lasers, or any other tools you might get a higher precision but you’ll never know the true measurement.
There will always be a range of values that can result from correctly and legitimately applying any measurement procedure.
The process of measurement is considered the study of procedures or methods that are used to remove the blunders, account for systematic errors and reduce the errors created by random events.
If you want to avoid mistakes, there are a few things you can do. Repeating measurements and keeping an eye on the results are just two of them.
Technically, systematic errors are unexplainable. That said, there are ways to account for such errors. One way is by standardizing the equipment used in experiments. Understandings of the effects of the environment can also help eliminate such errors. Finally, analysis of results will reveal any potential deviations due to systematic errors.
There are three ways by which the effects of random errors can be reduced: refining instrumentation, increasing observation volume and counting analysis. This process in the modern land survey is discussed in detail below.
The land survey is a complex process that requires the use of advanced technology to help take measurements for measured surveys, setting out, monitoring and topographical surveys. Even in the advent of satellite imagery and GPS technology making it easier to collect the data, we provide a better precision but things will never be true measures but better accuracy and higher precision (Depending on the equipment).