830-515-2002

Basic Surveying Techniques

Before building any outdoor structure near a neighbor’s land, be sure you know exactly where your property lines lie. Start by studying the lot plat, or map, that was furnished with the title to the land. When mapping the land, the surveyors drove metal stakes into the ground at the corners of the plot to serve as property markers. If you can locate one of them, your property map and a little basic geometry will enable you to find the others. You can determine the boundaries by driving stakes next to the markers, then stretching string between the stakes.

Once the boundaries are established, a few simple surveying techniques and tools will enable you to map the location and size of the structure you want to build. Distances can be measured fairly accurately with a mason’s line, wooden stakes, and a carpenter’s tape measure, but keep at least 12 inches from a property line when siting a structure to avoid accidentally straying onto a neighbor’s land. To sight lines for pouring foundations, or to establish perfect parallels or right angles to property lines, use a transit level.

TOOLS Tape measure Maul Shovel Magnetic stud finder Transit level MATERIALS Wooden stakes Tall poles Powdered chalk Mason’s line Clear plastic hose

CAUTION

Before positioning or excavating trenches, find the locations of underground obstacles such as dry wells, septic tanks, and cesspools, and electric, water, and sewer lines.

FINDING PROPERTY MARKERS

FINDING PROPERTY MARKERS

Working from two known markers

With a maul, drive a wooden stake next to a known marker. (Property markers may be lost in undergrowth or a few inches underground.) Attach a length of mason’s line equal to the distance between the known marker and the lost marker, as indicated on your property map. Mark an arc on the ground near the lost marker with powdered chalk (left). Repeat the procedure at another known marker. Dig for the lost marker at the intersection of the arcs (inset).

Working from a single marker

Mark an arc on the ground with chalk over the approximate location of the hidden marker (above). Brush a magnetic stud finder along the arc (right). When the stud finder’s needle deflects, dig for the marker. If the stud finder does not work, try using a metal detector. The final recourse is to call in a professional surveyor to reestablish the property lines.

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SIMPLE SIGHTING AND LEVELING TECHNIQUES

SIMPLE SIGHTING AND LEVELING TECHNIQUES

Sighting a straight line over a hill

Drive a stake at both the starting and unseen points. Stand at one stake, station a helper at the other, and have two more helpers hold tall poles in between at points where the tops of the poles can be seen from both stake positions (right and inset). Sighting from your stake, signal the pole holder nearest you to move until the two poles are in a straight line from your view. Have the helper at the unseen point repeat the procedure with the second pole person. Alternate sightings until the poles appear in line from both positions. Connect the four points with mason’s line.

Finding level points on a slope

You can find a point on a stake or post that is level with a mark on another by using a water level or a clear plastic hose partly filled with water. Make a mark at the desired or known height on the first post. Position the hose between the posts as shown. Hold one end a few inches above the mark you have made and have a helper hold the other end at about the same height. Fill the hose with water until the level reaches the mark. Make sure there are no air bubbles—if there are, block and lower one end to allow the bubble to rise to the surface. Finally, mark the second post at the water level in the hose (left).

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A TELESCOPE THAT MEASURES ANGLES

A TELESCOPE THAT MEASURES ANGLES

Anatomy of a transit level

This professional surveying tool is essentially a tripod-mounted movable telescope with precise scales for reading vertical and horizontal angles. The 20-power telescope pivots at its center for vertical measurements and the entire mounting carriage rotates on the undercarriage for horizontal ones. A small spirit level mounted under the telescope assists in leveling and plumbing the instrument. A hook for a plumb bob hangs from the base plate; the undercarriage slides over the base plate to position the bob over a stake or marker, and four leveling screws are used to set the level. Angles are measured on vertical and horizontal scales; when only horizontal measurements are needed, as on the following pages, a pair of levers locks the telescope in the level position. Slow-motion screws allow you to zero in on the sighting stake by turning the telescope; clamp screws then lock the transit in position.

DIFFERENT SCALES FOR DIFFERENT ANGLES

DIFFERENT SCALES FOR DIFFERENT ANGLES

In addition to setting straight lines or right angles (page 166), a transit level can be used to measure a range of horizontal and vertical angles. Horizontal angles are read on a 360-degree circular scale divided into four 90-degree arcs (top left), vertical angles on a 90-degree arc (bottom). Small auxiliary scales called verniers serve as pointers for the main scales and give readings in sixtieths of a degree, or minutes.

If the zero mark on the vernier falls between two degree marks on the main scale, read the lower mark and use the vernier to calculate the fraction in minutes. Reading upward from the degree mark, find the mark on the vernier that lines up perfectly with a mark on the main scale. Count the vernier spaces between the two main-scale marks. Each space stands for 5 minutes; multiply the number of spaces by five to get a reading in minutes. The sighting at right reads 17 degrees 15 minutes.

SETTING UP A TRANSIT LEVEL

SETTING UP A TRANSIT LEVEL

Positioning the tripod

Spread the tripod legs over a marker to be used as a starting point. Move the legs one at a time until the plumb bob hangs no more than ¼ inch from the center of the marker. Loosen the screw under the base plate and shift the transit level so the plumb bob is directly over the center of the stake. Tighten the base-plate screw.

Leveling the transit

Set the vertical scale to zero. Loosen the horizontal clamp screws and turn the telescope until it aligns with one pair of leveling screws. Turn these screws until the bubble in the level is centered (left). Rotate the telescope 90 degrees to align it with the other pair of screws; adjust these screws the same way. Repeat as needed, making minor adjustments so the bubble in the level remains centered as the telescope swings full circle.

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A LASER TRANSIT

A LASER TRANSIT

The laser transit replaces the telescope of a traditional transit by emitting a laser beam, which enables the device to be used by one person. A traditional transit requires two people—one at the telescope and another at the target. But the laser transit can be aimed by the user who can then go to the target and observe the beam.

PRECISE LINES AND ANGLES

PRECISE LINES AND ANGLES

A line over a long distance

Drive stakes at the two points to be aligned and prepare an intermediate sighting pole for each of the major peaks and valleys between the stakes. Position and level the transit over the starting stake as shown on page 168. Focus on the far pole and tighten the horizontal clamp screw. Have a helper hold the furthest intermediate stake at its approximate position (right), moving it until it is centered in your field of vision, then drive the stake into the ground. Repeat the procedure for the other stakes.

Setting a right angle

Set a straight line to a stake, as shown here. Rotate the transit level exactly 90 degrees on the horizontal scale and tighten the horizontal clamp screw to lock it in position. Have a helper move another pole until you sight it in the cross hairs (right), then drive the pole in place. Check the angle by swinging the transit level back 90 degrees to the original pole and ensuring it is sighted in the cross hairs.

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SIGHTING A PARALLEL LINE AROUND AN OBSTRUCTION

SIGHTING A PARALLEL LINE AROUND AN OBSTRUCTION

Plotting an approximate parallel

You may need to set a line parallel to one that is obstructed, such as property line A-B in this example. Set up the transit over a starting stake where the view is unobstructed and sight a line roughly parallel to line A-B (above). On this line, drive a stake at point D so that lines A-B and C-D are equal in length. Stretch a mason’s line between points C and D.

Locating the first stake

From point C, rotate the transit 90 degrees toward point A. Move the transit along the mason’s line so that the cross hairs align with the stake at point A (left). Rotate the transit 90 degrees toward point D to line up the cross hairs with the stake; adjust the position of the transit as necessary, so that it rests at the apex of a 90-degree angle between points A and D. Drive a stake directly underneath the transit—at point E.

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Locating the second stake

Measure the distance between points A and E, and cut a length of the mason’s line equal to that distance. Attach the line to the stake at point B and swing it toward point D, making an arc. Loosen the line joining points C and D, fasten one end to the stake at point E, and swing the other end in an arc toward point D. Plant a stake where the two arcs intersect (point F). The line joining points E and F is now parallel to the property line between points A and B.

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