Bihar Special Survey Amin flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Plane vs geodetic survey

Plane surveying treats the earth's surface as flat and is used for areas under about 250 square kilometres. Geodetic surveying accounts for curvature and is used for larger areas and precise control networks.

Representative fraction (RF)

The ratio of map distance to ground distance, written as 1:n. An RF of 1:2500 means one centimetre on the map equals 25 metres on the ground.

Gunter's chain length

A Gunter's chain is 66 feet, or 20.1168 metres, and has 100 links. Each link is 0.66 feet, and 80 chains make one mile.

Acre to hectare

One acre equals 4840 square yards, 43,560 square feet, or 4046.86 square metres, which is 0.404686 hectare. One hectare equals 10,000 square metres or about 2.471 acres.

Systematic vs accidental error

Systematic errors follow a fixed rule, accumulate in one direction, and are corrected by calibration. Accidental errors are random, small, and reduced by repeating observations and averaging.

Chain correction formula

When a chain is too long or too short, correction per chain equals (true length minus nominal length) divided by nominal length, multiplied by the measured length.

Prismatic compass bearings

The prismatic compass gives quadrantal bearings measured from magnetic north or south toward east or west, between 0 and 90 degrees. Fore bearing minus back bearing equals 180 degrees.

Local attraction detection

Local attraction is detected when the difference between fore bearing and back bearing of a line differs from 180 degrees. Readings at the affected station are corrected using unaffected lines.

Dumpy vs tilting level

A dumpy level has the telescope rigidly fixed to the levelling head. A tilting level lets the telescope tilt slightly so the bubble can be centred quickly for each reading.

Automatic level compensator

An automatic level replaces the bubble tube with a compensator using prisms or mirrors. It automatically keeps the line of sight horizontal within its working range after rough levelling.

Well-conditioned triangle

A triangle used in chain surveying whose angles lie between 30 and 120 degrees. No angle should be below 30 degrees, and the base line should be the longest side.

Plane table radiation method

The table is set at one station and rays are drawn to all objects, with distances scaled along each ray. It suits small areas where all objects are visible from one point.

Three-point problem

Fixing the plane table position from three known points by trial and error, tracing paper, or Bessel's graphical method. It is a case of resection used when the station is unknown.

Offsets in chain surveying

Perpendicular distances measured from the chain line to objects. Offsets up to about 15 metres may be set by eye; longer ones need a cross-staff or optical square.

Height of instrument

The reduced level of the line of collimation, equal to the reduced level of the benchmark plus the backsight reading. Reduced level of a point equals HI minus the staff reading.

Rise and fall arithmetic check

The sum of backsights minus the sum of foresights equals the sum of rises minus the sum of falls, which also equals the last reduced level minus the first.

Curvature and refraction correction

Curvature correction is 0.0785 d squared metres with d in kilometres. Refraction is about one-seventh of curvature, so the combined correction is minus 0.0673 d squared metres.

Contour interval choice

The vertical distance between successive contours. A small interval suits flat ground and detailed work; a large interval suits steep terrain and reconnaissance mapping.

Reciprocal levelling

Levelling from both banks of a river or valley and taking the mean. It eliminates errors from curvature, refraction, and imperfect instrument adjustment.

Face left and face right

Two observations of the same target with the telescope in normal and reversed positions. Averaging both faces eliminates collimation, trunnion axis, and vertical axis errors.

Theodolite fundamental lines

The vertical axis, horizontal or trunnion axis, line of collimation, and bubble tube axis. In a correctly adjusted instrument these lines hold fixed perpendicular or parallel relationships.

Closed traverse angle check

For a closed polygon with n sides, the sum of interior angles equals (2n minus 4) times 90 degrees. The sum of exterior angles equals (2n plus 4) times 90 degrees.

Latitude and departure

Latitude equals length times cosine of the reduced bearing, positive for northing. Departure equals length times sine of the bearing, positive for easting.

Bowditch rule

A traverse adjustment rule that distributes total latitude and departure misclosure in proportion to the length of each side. It suits surveys where angular and linear errors are comparable.

Transit rule

A traverse adjustment rule that distributes misclosure in proportion to the latitude or departure of each side. It is used when linear measurement is more precise than angular measurement.

Khatiyan and Jamabandi

Khatiyan is the record of rights listing the tenant, land, and nature of right. Jamabandi is the working account of rents and dues maintained in Bihar land records.

Cadastral map scale

Cadastral maps in India commonly use scales of 1:1000, 1:2000, or 1:4000. Densely built urban parcels use larger scales for boundary clarity.

Field book discipline

Entries are made in pencil at the time of survey, with no erasures. Mistakes are struck through and rewritten with initials so the record remains legally reliable.

Simpson's rule

For an odd number of equally spaced ordinates, area equals h divided by 3, times the sum of the first and last ordinates plus four times the odd ordinates plus twice the even ordinates.

Heron's formula

The area of a triangle with sides a, b, and c equals the square root of s times (s minus a) times (s minus b) times (s minus c), where s is half the perimeter.

Kosi river flood reputation

The Kosi, a Himalayan river in north Bihar, is called the Sorrow of Bihar because of its shifting course and severe floods. The Gandak and Bagmati also flood the plains.

Bihar land revenue authority

Bihar's land records and survey settlement are administered by the Department of Revenue and Land Reforms, with the Board of Revenue and district officers supervising field operations.