Surveyor's Footsteps: How Close Should Survey Measurement Be?
Recently, my apprentice asked me “How close is close enough?” That question has many answers, which depend on the specific object we are locating and why it is being located. I believe it is a very important aspect of land surveying and takes many years in the field to get a handle on that complex answer. As kids, we liked using the expression “Close enough for hand grenades.”
While rough staking a house with my other apprentice, we were putting wire flags at the proposed corners of the house. The contractor wanted only four “box” markers to start, and would call me back for stakes at the location where I was now setting wire flags. With a robotic instrument, it takes so little time to set wire flags because they only need to be within a tenth of a foot to be very accurate. I motioned to her to look at the earthmoving machine and said, “These only have to be close enough for a bull dozer.” When the basement is hogged out, we will go back and set building corners more accurately.
At my first place of employment, back in the 70’s, they were using three- or four-man survey crews. (It would be many years before I saw women in land surveying) While I was filling in on a crew that was very productive in construction stakeout, I had the privilege of learning from the oldest rodman I will ever see.
Paul had been a union worker at the local Chrysler plant. When discontent arose among the ranks, his coworkers urged Paul to spearhead the issues. I do not know what happened with those complaints, but I do know that he found himself out of a job. After that, Paul vowed never again to rock the boat, and so avoided becoming a transit man or party chief and perfected the position of rodman. He was a hard worker and a skilled tradesman. He did not complain about anything.
At 18, Paul saw me as an empty-headed teenager as far as surveying was concerned. He took the time, whenever the party chief was busy, to teach me the fine points of being a rodman. Being as I knew little about land surveying, I listened closely. Paul knew the proper way to tie flagging onto a lath. You may think, “Is there really any proper way to tie on flagging?” Yes, there is. Poorly tied, flagging drops to the ground quickly.
The problem with writing is that you can’t see what I am trying to describe. Seeing it done is the advantage of a journeyman approach to land surveying. This I can say, you wrap the flagging twice around the stake and tie it at a corner of the stake. You do this after you drive the stake into the ground or the flagging will come off the stake as it is hammered. If it is freezing out, and the flagging is brittle and snapping, you lean down and breathe on the place where you will tie the knot to warm the flagging. When you tear off a length of flagging, make it long enough to blow in a gentle breeze but not so long that it drags on the ground, preventing it from fluttering and telling everyone “here I am!” When you take the sum of many such small techniques, it makes a difference. If you think that is a description of everything about tying on flagging, you are wrong. There are many styles of brush strokes a painter uses as there are also many ways we use our flagging.
One more thing I specifically recall Paul teaching me was, when we have set a hub or pin and want to mark it with a protecting stake, to put the side of my foot almost touching the marker, and then putting the lath on the other side of my foot. He said, “If you put it too close, you could move the hub.” Makes sense? I think so, but I am noticing many surveyors who drive a lath against pins they have found or have set. Perhaps the disconnect from a video game life to a construction life leaves young people not realizing that in this physical world they are moving the marker, even if it is a small amount.
When we perform boundary surveys, we work to plus or minus 0.01 ft. while locating pins and monuments, so that if there is some loss of accuracy, it is minimal. If you set a hub with that precision, only to move it 0.02 ft. when the lath pushed it to the side, you have taken your last chance to screw things up. If it moves 0.04 ft. a carpenter will notice when they check your hubs and make mental notes about the quality of your work. “Back in the old days” we would set four hubs on a house stakeout and then measure the diagonals. All good layout people know this, but today, with radial stakeouts and GPS satellites, how many will even measure between two points on footings?
I recall nailing some footers for a contractor who hired a foundation crew from another country. Please do not think that I have any notion that non-Americans are poor basement builders. At that time, the one fellow who spoke English was not there. I noticed them unintentionally banging my hubs around and I would fix them. I tried to explain they needed to stop hitting the markers. They looked back like deer in headlights, and I knew it was useless. Therefore, I documented my stakeout and made notes about workers not taking care to keep off my points. Before leaving the site, I fixed a few more hubs, which they had hit. The contractor never called to complain so I guess even after they had their way with my hubs and tacks, their foundation was “close enough.”
After performing an as-built survey out in Independence, Missouri, we measured up the house foundation. My picture in the notes was nice enough and when done measuring I checked the work by adding up the width of the house at the front and back to see that the added distances matched. They did not. So just before taking a third set of measurements, a carpenter who had been watching us from a higher story of the house leaned out and said “It doesn’t measure up, does it?” Turning up to see him leaning out the window opening, I said “No.”
He explained that when they were setting up the forms for the foundation, they made one wall four inches too long. This error was tough on the construction crew as they were well into framing as they went through mental gymnastics attempting to make things fit before they figured out why things were not working out. The framing, drywall, and roof were custom built to correct the foundation error and he said it was not easy to do. The skill of the construction people made four inches “close enough,” but I bet that foundation crew heard many harsh words and never did that again. They were fortunate the contractor did not make them tear it down and do it right.
Not far from my office here in Pennsylvania, I prepared a topographic survey plan for a contractor and his client. From that plan, I took the proposed house from the architect’s drawings and placed it on the lot and indicated the existing house was to be demolished. When the Building Permit Plan was approved by the township, I was called upon to stake out the new house. Once I had put in a few markers, the contractor stopped me and wanted to talk.
Although the existing house was to come down, they were going to utilize the existing septic system and well. The contractor saw the relationship of the well to the front of the new house and was concerned if one day they needed to pull the submersible pump out of the well, did they have enough room between the proposed house and the existing well. That was the time to move the house farther back if necessary. They called upon the man who installed the well to ask how far the well needed to be from the front of the house so that a crude hoist tripod could be placed over the well and a rope and pulley implemented to pull up that old pump and lower the replacement. If it was too close to the house, it could make that change difficult. Thinking of these very things is what experience gives us.
When performing boundary and topographic surveys, I take time to explain to my apprentices some of the reasons why accuracies could be diminished by poor field procedures and when and why accuracy may not matter. How accurately does a tree need to be located? A well cap? A water valve? There are so many different things to locate and we do not want to locate them all as closely as a rebar. To speed up an apprentice, I started to take spot shots reflectorlessly, over a parking lot without even looking through the instrument. Later in the day, I demonstrated spot shots on grass and my not even looking at the bubble to see if it was level. In various instances, I may ask, “If this edge of pavement location was an inch away, would it make a difference?”
As I teach everyone to do the drafting for their own fieldwork, they will learn early about the “scale” of a drawing. Most people have not been using a scale before actually working in land surveying or engineering. They will learn about ten scale and eighth scale drawings and see that you can actually scale a few inches on a print and so must consider what they are locating and who will be using the information. Therefore, for a ten-scale plan, I am careful to locate items more accurately. The scale of a drawing is a whole subject in itself.
Frankly, I thoroughly enjoy teaching apprentices all about land surveying. In rural tracts, residential lots and homes, and construction, there are so many variables. My employees having a deeper understanding of the work keeps me out of trouble. Whenever we teach our employees new things, we invest in our business, our future and the future of land surveying.