Accuracy, precision and boundary retracement in surveying

July 5, 2017  - By 6 Comments

Technology has improved the scientific community’s ability to measure in many ways that our ancestors would have trouble believing. From obtaining measurements across galaxies down to the tiniest of atom splitting, our ability to measure is exceedingly robust. The land surveying profession has benefitted from this ongoing technological revolution in many ways (GPS World March 2017) and has advanced our work in many new directions never thought possible. Substantial increases in precision through these advancements allows the land surveyor to perform various tasks, including topographic surveys, construction layout and volumetric surveys with increased confidence.

Accuracy and precision are two factors that go into our measurement procedures. While accuracy and precision are considered to be the same thing by a large portion of the population, it couldn’t be more from the truth. Accuracy is defined on how well a measurement or reading is in relation to a known value or benchmark. Precision, on the other hand, is how closely a measurement is repeated yet has no relation to any given value or benchmark.

The introduction of GNSS technology along with total stations with locking electronic distance measuring (EDM) mechanisms in the 1980’s brought more precision into the hands of the surveyor. These innovations reduced the amount of human error in our measuring procedures when used in an appropriate manner as well as allowing greater distances to be covered. The implementation of various real-time networks (RTN) on several continents also continues to increase our range of high-precision location and measurements worldwide. However, as we develop our next generation of surveyors through educational programs and apprenticeships, we are making a terrible mistake in replacing many fundamental land surveying principles and legal precedents with more emphasis on precision and less on legal accuracy based upon precedents.

Surveyors and the role of measurement

In ancient civilization, the primary role of the land surveyor was to help establish and maintain property boundaries. Measurement devices included knotted rope, the Gunter chain and the compass, all used is varying manners and precisions. Paramount to the surveyor’s effort was the establish of monuments at corner points of the tracts they were measuring. These points were held as the ultimate dividing point and superior to associated measurements and secondary tie points. This simple guide for all surveyors has been a core principle of property owner’s rights and upholding those rights in the name of the law. By placing of monuments, the landowner has relied on the surveyor to physically define the property being established and conveyed.

Let’s ask Washington, Jefferson and Lincoln…

For example, in early days of the United States during the late 1700’s/early 1800’s, once an original survey was completed, notes of each survey were preserved by various means. Most governmental surveys of the early 1800’s were transcribed onto large township sheets in order to perpetuate and preserve the work performed by the Land Office surveyors. The establishment of states and local governments brought forward land and records offices in which these government patent lands were further subdivided for conveyance to settlers of the new lands. In each of these cases, corners of various types were set to distinguish boundaries between property ownership. Wooden posts, rock mounds, and other materials were used to physically mark the locations of the corners, with notes, documentation and deeds for conveyance coming after the determination of the property. Regardless of any variation from the notes/plats/deed descriptions, property rights were held to the physical locations of the markers set during the course of the survey.

The American dream of land ownership

As more people moved westward and parcel subdivisions became more prevalent, planned developments began to be based upon pre-calculated figures. Before calculators and computers, the surveyor would determine the location of new parcel corners by hand derived calculations (usually in the field) and use a transit and chain to stake each parcel corner. Notes were carefully kept during the lot creation process and transferred to a final plat for filing at the county recorder’s office. These plats were typically post-survey with the detailed notes being drawn on the plat with specific dimensions to all points set.

As plane geometry and coordinate systems caught on (GPS World November 2016), the movement toward pre-calculated subdivisions became more common. Couple this method of calculation with increased capability of high precision theodolites and the World War 2 postwar boom, the economy and environment was ready for more time efficient surveys. Now large parent parcels were being subdivided on paper before any additional surveying was performed to establish the new lotting configuration. Surveyors began to stake parcel corners by means other than “running the lines”, i.e. physically occupying the outer boundary and setting internal points for new parcels. Add to this environment of “faster” surveying the invention of the EDM, digital total station, computer programming and analysis along with GNSS, and now we have a recipe for the most precise and accurate surveying ever performed. Or do we?

These are not your father’s (or grandfather’s) survey methods anymore

Regarding topographic, volumetric, bathymetric and aerial surveys, I would agree that technology has advanced our profession to greater heights. These tasks have benefited greatly by increased data collection, remote location and sensing and computing power. The surveyor’s ability to provide an extremely detailed set of data for varying surfaces and site conditions is at an all-time high with more technology continually being developed. But how has technology affected our primary role of boundary line expert? While in many ways as technology has helped the boundary survey, it has also taken away from the surveyor’s responsibility and duty as expert measurer. The intent of the surveyor is mostly clear when retracing a prior survey or creating new parcels from existing ones but execution, along with mistakes/errors/blunders, throw ambiguity into the fold. Not knowing where to find a random error within a prior survey leads many practitioners down a long and frustrating path. In a perfect world, the math would all work out and everything fits together like a glove. However, due to many variables and errors that randomly and systematically happen during our work, this condition is near impossible to attain. This quote is from the “Illinois Boundary Law” book written by land surveyor/attorney Jeff Lucas in 2012 sums it up well:

“There is an irresistible urge on the part of many surveyors to trust math and measurements over their understanding of boundary law principles. When this misplaced trust is coupled with the confusion over the land surveyor’s duties and responsibilities, the land surveyor is free to ignore clear-cut doctrines of law when precision expectations come into conflict with the realities that are found on the ground.”

So, what does this mean? Many of the legal descriptions surveyors have been charged with to perform a boundary survey were created using equipment, techniques and simple math far inferior to today’s standards. For example, a survey in downtown Chicago may be based upon a plat from the early 1800’s, (if the record happened to survive the Great Fire of 1871) and was depicted in chains and links. We now have surveyor who show all dimensions to the 1/1000th of a foot on these boundary and land title surveys. Considering that most of the surveys from that era only had a precision of one link (0.66 ft.), it could be considered overkill to need to be that precise. I’m in agreement that the survey must depict the current conditions and properly define where boundary rights are physically located, but to show that many significant figures is careless and unnecessary.

For surveys on larger parcels and in rural areas, GNSS use (and abuse) now comes into play much more often. As I’ve written previously (GPS World May 2016) GNSS implementation is the single greatest advancement of surveying technology in my opinion. The ability to survey significant areas with great precision still impresses me and I wouldn’t trade it for anything. But notice I stated “precision” and not accuracy and this is where many surveyors get off track; hence, the statement from Mr. Lucas.

You’re not the original; you’re the retracement

While a small proportion of surveys completed today are for government lands and follow the Bureau of Land Management’s Manual of Surveying Instructions (2009 Edition), the remaining surveys are broken into two categories by whom they are performed by: the original surveyor or the retracement surveyor. This is best described from the text of the well-known Florida court case of Rivers v. Lozeau (539 So.2d 1147 (Fla. App. 5 Dist. 1989):

“First, the surveyor can, in the first instance, lay out or establish boundary lines with an original division of a tract of land which has theretofore existed as one unit or parcel. In performing this function, he is known as the “original surveyor” and when his survey results in a property description used by the owner to transfer title to property that survey has a certain special authority in that the monuments set by the original surveyor on the ground control over discrepancies within the total parcel description and, more importantly, control over all subsequent surveys attempting to locate the same line.

Second, a surveyor can be retained to locate on the ground a boundary line which has theretofore been established. When he does this, he “traces the footsteps” of the “original surveyor” and locating existing boundaries. Correctly stated, this is a “retracement” survey, not a resurvey, and in performing this function, the second and each succeeding surveyor is a “following” or “tracing” surveyor and his sole duty, function and power is to locate on the ground the boundaries corners and the boundary line or lines established by the original survey; he cannot establish a new corner or new line terminal point, nor may he correct errors of the original surveyor. He must only track the footsteps of the original surveyor. The following surveyor, rather than being the creator of the boundary line, is only its discoverer and is only that when he correctly locates it.”

The surveyor’s role in boundaries, period

To further illustrate the surveyor’s role in each type of survey, let’s examine the recent publication of “Boundary Retracement Processes and Procedures” by Donald A. Wilson, a long-time land surveyor and prolific writer of surveying manuals. Don’s book delves deep into all things concerning the role of the land surveyor in completing a property retracement survey. While surveying does rely heavily on good measurement techniques, it goes along with a handful of other talents as well. Don’s book revisits a 1985 Vermont Society of Land Surveyor’s publication “Cornerpost” (VSLS Cornerpost) that contained an article titled “What does a land surveyor do?” written by George F. Butts. In the article, George lists in detail that besides the prerequisite surveying knowledge, the surveyor must also have some aspect of skills for the following disciplines: archaeologist, astronomer, cartographer, computer specialist, dendrologist, detective, engineer, farmer, forester, geologist, handwriting expert, historian, hydrologist, lawyer, logger, judge, juror, photogrammetrist, writer, and expert witness. Notice that George didn’t include mathematician or statistician, both disciplines that rely heavily on the study of formulas, figures and data. While surveying computations relies heavily on geometry and trigonometry, the first order of business in data analyzation is how it relates back to the “original survey.” This brings us back to the primary role of the land surveyor – “following the footsteps.” As Don quotes; “…following the footsteps of the original surveyor is the legal standard adopted by the courts in all jurisdictions, and for very good reason.” The intent of the retracement surveyor is to uncover the past through all necessary information and bring to life the original survey. How the surveyor gets there, through the muddied use of technology, often leads us down the wrong path. He also adds from the 1818 South Carolina court case of Bradford v. Pitts (2 Mills. Const. Rep 115); “Blind devotion to a rule may lead to infinite failure.”

Back to the Stone Age?

So, what is the answer? Do we throw out all the electronic tech and time-saving methods in order to retrace all surveys with compass and/or transit and chain? Of course not. I do ask that all surveyors look at what the profession has charged them with and how they use their tools to get there. For instance, I am thankful for all the medical breakthroughs in the past 100 years, especially when it comes to technology. Imaging machines, robotic laser procedures for internal surgeries and more come to mind, but let’s remember that doctors still look at the human element and not just what a computer spits out as a diagnosis. How many times have you looked up your symptoms on WedMD and decided you were dying from that rash? Surveyors are doing the same thing with analyzing data from the mathematics view and not from the boundary law principles view.

It’s not all just about the location data

High-precision GNSS locations (and conventional data) we collect as surveyors needs to be included with the analyzation of the historical data from the legal side of the survey. If we didn’t find the original points, did we find ones that were substantially close to where the originals were? Were any of the original conditions at the time of the survey still intact? Bearing trees? Buildings? Any reference ties? What most surveyors tend to forget well is that all measuring devices (and I do mean ALL) are not the same, no matter how close they are manufactured and calibrated. Couple that with mistakes/errors/blunders I spoke of earlier, and here is your recipe of inconsistencies between surveys. You will say your instruments and devices are in top condition, so your data is right and the previous surveyors obviously messed something up. The unfortunate thing is that almost every surveyor makes that statement and we all are wrong to some degree. The bottom line is that while we may collect a ton of data with the upmost precision, it may not be accurate with the intent of the project, which is to retrace the original survey to the best of your ability. I’m not advocating that we dump our fancy robots, our very handy RTN networks or my shiny new UAV; instead, let’s get back to the basics. As Don Wilson notes in his preface of the new book; “One of the biggest differences between the surveyor relying on principles and court relying on precedent is that courts continually revisit the reason for the rule, or the decision in the previous case, to ensure that it applies, and fits the issue.” What I am advocating is that we remember the duties of our role and utilize the necessary tools to perform and deliver to the best of our abilities. I’ve had mentors and teachers that relied heavily on the math and not so much the true legal definitions. That means we need to brush up on the law and precedents that have been established for various situations and reasons. It will be through continuing education of our everchanging profession that will open more surveyor’s eyes to what the role of the surveyor was truly meant to be. With no disrespect to the GIS world, surveyors don’t aspire to be a map makers or database managers. We are professional land surveyors and our duty to our clients includes professionalism and the completion of an accurate land survey through precision measurement and analysis. Just as long as we follow those footsteps…

6 Comments on "Accuracy, precision and boundary retracement in surveying"

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  1. Jarrod Black says:

    Thoroughly enjoyed reading this article. Given the amount of useless information available to enlighten the mind these days, this was well worth my time.

  2. Joe Beyers says:

    Great article Tim. Always educational and very informative. Couldn’t agree more. The county of Christian here in Illinois has had some excellent “retracement” surveyors in the past following the original surveys. We’re still finding stones and noted posts per original surveys found in the recorders office. I love this profession and always learning more of the past to preserve the present/future land owners of Illinois. Thanks!

  3. Kskaliprasad says:

    Very good article. Thought provoking.

  4. Kskaliprasad says:

    Very good article.

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