FS Surveying key terms

A reference surface or set of parameters against which positions or elevations are measured; horizontal datums define coordinates on an ellipsoid, and vertical datums define heights above a zero reference surface.

The equipotential surface of the Earth's gravity field that best approximates mean sea level and is imagined to continue through the continents; it serves as the zero reference for vertical datums.

A mathematically defined flattened sphere used as the reference surface for horizontal coordinates, with size and shape chosen to fit the geoid globally or over a region.

A relatively permanent, stable object whose elevation above a vertical datum has been determined by survey, used as a starting or checking point for leveling operations.

The angular difference at a given place and time between magnetic north, as indicated by a compass, and true or geographic north; it varies with location and changes slowly over the years.

A system of planar rectangular coordinates defined separately for each state or zone by map projection from the national horizontal datum, allowing surveyors to compute and record positions in feet or meters.

An electronic instrument that combines an electronic theodolite, an electromagnetic distance meter, and an onboard computer, so angles and distances to a target are measured and recorded from one setup.

An optical or electronic instrument for measuring horizontal and vertical angles precisely, consisting of a telescope rotating on horizontal and vertical axes fitted with graduated circles.

A sight taken to a previously known point in order to orient the instrument, establish a reference direction, or determine the height of the instrument before other measurements are made.

A sight taken to a new point whose direction, position, or elevation is to be determined; in leveling it is the rod reading taken on a point ahead of the instrument.

A temporary point on which a leveling rod is held so the instrument can be moved and set up again while a leveling line continues, carrying the elevation forward.

The elevation of the line of sight of a leveling instrument above the chosen datum, obtained by adding the backsight rod reading to the known elevation of the point sighted.

The procedure of determining elevation differences between points by reading a graduated rod through a level from setups between them, accumulating backsight and foresight differences along the line.

A survey in which the lengths and directions of a connected series of lines are measured so that the positions of the stations at the ends of those lines can be computed.

The horizontal angle measured clockwise from a chosen reference meridian, usually north, to a given line, taking values from zero to 360 degrees.

The acute horizontal angle between a reference meridian and a line, always stated with a quadrant label such as N 45 E or S 30 W.

The northing and easting components of a traverse course, calculated as the course distance multiplied by the cosine and sine of its azimuth respectively.

The amount by which a survey fails to return to its known starting value or known point, such as the gap between the computed and known end positions of a closed traverse.

A method of distributing measurement errors by finding the coordinates or values that minimize the sum of the squares of the weighted residuals, yielding the most probable solution.

How close a measured or computed value is to its true value; it is degraded mainly by systematic errors and is distinct from the scatter of repeated measurements.

The degree of repeatability or consistency among repeated measurements of the same quantity, reflecting random scatter; a highly precise result can still be inaccurate.

A method of describing land by giving the courses and distances of its boundary lines, usually beginning and ending at a known monument or point of reference.

A physical object, either natural or artificial, that is placed or accepted to mark a boundary corner or survey point and that controls the location described in a deed or plat.

A survey performed to re-establish or verify the boundaries of an existing parcel as originally created, relying on record evidence and original monuments rather than establishing new lines.

The rectangular system used to subdivide public lands in the United States, laying out township and range lines at six-mile intervals and dividing townships into sections and aliquot parts.

A right held by one party to use a defined portion of another person's land for a specific purpose, such as access or utilities, without owning that land.

The rights belonging to owners of land bordering a stream, river, or lake to use and access the water and, under some rules, to land that gradually accretes.

A legal doctrine under which a person who openly, notoriously, exclusively, and continuously occupies another's land for the required statutory period may acquire title to it.

The apparent shift in an object's position relative to a reference when it is viewed from different locations; in photogrammetry this displacement lets distances and elevations be derived from overlapping photographs.

A photograph that has been differentially rectified to remove displacements caused by camera tilt and terrain relief, giving it a uniform scale so it can be used like a map.

A point on the ground whose horizontal position or elevation is known and which can be identified on imagery, used to orient, scale, and georeference photogrammetric or remotely sensed data.

A remote sensing technique that measures distances by timing laser pulses reflected from the ground or from objects, producing dense point clouds used for terrain models and mapping.

A line drawn on a map or plat that connects points of equal elevation, so that the spacing and shape of the lines portray the steepness and form of the terrain.

A map of a land parcel or subdivision showing boundary lines, dimensions, monuments, lots, streets, and any dedications, prepared for recording in the public land records.

The relationship between a distance measured on a map and the corresponding distance on the ground, expressed as a ratio, an equivalence, or a graphic bar scale.

A parabolic curve used to join two intersecting grades on a roadway or other alignment, providing a gradual change of slope that is safe and comfortable to travel.

The earthwork of excavating soil where existing ground lies above the design grade and placing it where ground lies below, bringing the terrain to the planned elevation.

The field operation of marking on the ground the horizontal positions and elevations of planned design elements, such as building corners, pipes, or roadway centerlines, for the construction crew.

A survey performed after construction to record the actual horizontal location and elevation of improvements as they were built, so results can be compared with the design drawings.

The degree of care, skill, and diligence that a reasonably prudent surveyor, practicing in the same locality and under similar circumstances, would exercise in the same work.