BTEB Amin Survey Exam key terms

A method of land measurement in which distances between stations are measured with a chain or tape, and details are located by offsets from these measured lines. Angles are rarely measured directly.

The longest and most carefully measured line of a chain survey, forming the backbone from which the whole framework of triangles is built and to which all other measurements are referred.

A survey line joining two fixed stations or points on the main framework but not forming part of a principal triangle, used to check or strengthen the survey.

A line measured between two already fixed points to verify that the plotted framework is correct. Any disagreement between measured and plotted length reveals an error.

The perpendicular or oblique distance measured from a survey line to a detail such as a boundary, building corner or tree, used to fix that detail's position on the plan.

An offset measured at right angles to the chain line, usually set out with a cross-staff or optical square. It is the shortest distance from the detail to the line.

A small hand instrument with two mirrors set at 45 degrees, used to sight a point on the chain line and simultaneously locate the direction of a line at right angles to it.

A simple instrument with two crossed sighting vanes set at right angles, used to range out a perpendicular to a chain line when setting offsets.

The process of fixing intermediate points in line between two survey stations so that a straight line can be measured accurately over long distances or across obstacles.

The horizontal angle measured clockwise from magnetic north to a survey line, expressed in degrees or as a quadrantal bearing such as N 30 degrees E.

A bearing measured clockwise from north through the full 360 degrees, so that every line direction is expressed as a single angle between 0 and 360 degrees.

A quadrantal bearing expressed as an angle less than 90 degrees together with a quadrant letter, such as S 45 degrees W, derived from the whole circle bearing.

The deviation of a compass needle from magnetic north caused by nearby iron, steel, electric cables or magnetic rock, detected when fore and back bearings differ by other than 180 degrees.

The horizontal angle between true north and magnetic north at a place, which varies with time and location and must be applied to convert magnetic bearings to true bearings.

A series of connected survey lines whose lengths and directions are measured, forming a framework from which the coordinates of each station can be computed.

The northing or southing (latitude) and easting or westing (departure) of a traverse line, found by multiplying its length by the cosine and sine of its bearing respectively.

The amount by which a traverse fails to return to its starting point or known closing station, found by combining the total latitudes and departures of all lines.

A method of adjusting a closed traverse in which the total error in latitude and departure is distributed in proportion to the length of each line, also called the compass rule.

A permanently fixed point of known reduced level, often a brass bolt or engraved mark on a stable structure, used as a reference for levelling operations.

The height of a point expressed relative to a chosen datum, obtained in levelling by adding or subtracting staff readings from a known height.

The first staff reading taken on a point of known reduced level after setting up the level, used to establish the height of the instrument.

The last staff reading taken on a point before moving the instrument, used to determine that point's reduced level and to close or continue the levelling operation.

The reduced level of the line of collimation of a level, calculated by adding the backsight reading to the reduced level of the point on which it was taken.

A line on a plan joining points of equal elevation, so that its spacing and shape show the steepness and form of the ground.

The constant vertical distance between successive contour lines on a map, chosen according to the scale of the map, the relief and the purpose of the survey.

A drawing board mounted on a tripod and fitted with a sighting alidade, used to plot survey lines and details directly on the sheet in the field.

A straightedge with a sighting device, such as a telescope or open sights, mounted on the plane table and used to draw rays to objects while sighting them.

A plane table method in which the instrument is set up at an unknown point and its position on the sheet is found by sighting two or three known stations.

The plane table problem of locating the instrument station on the sheet from rays drawn to three known points, solved by trial, tracing paper or geometric construction.

A plane table method in which the position of an inaccessible object is fixed by drawing rays to it from two or more known plotted stations; the rays cross at the object's plan position.

A method of computing area by dividing the figure into strips of equal width and summing the average of each pair of end offsets multiplied by the common interval.

A method of computing area from an odd number of equally spaced offsets, using one-third of the common interval times the sum of end ordinates plus four times odd and twice even ordinates.

An instrument that measures the area of an irregular figure on a plan by tracing its boundary with a pointer and reading the resulting value from a graduated wheel.

A volume formula using the areas of two end sections and the mid-section, giving the volume as one-sixth of the length times the sum of end areas, four times mid-area and the other end area.

The process of transferring a designed structure, road or boundary from the drawing onto the ground at its correct position, level and dimensions before construction begins.

A bound notebook in which all survey measurements, sketches and remarks are recorded in the field in ink, forming the permanent original record of the survey.

A plan on which contour lines are drawn to represent the relief of the ground, used for route selection, drainage design and earthwork estimation.