Introduction to surveying

This page is a short primer — not a full textbook. It defines surveying, its main divisions, how measurements are made, and the order of work in the field and office. For Andhra Pradesh cadastral procedure, use the guides hub and the toolkit calculators linked at the end.

1. What surveying and laying out mean

Surveying determines the relative positions of points on, above, or below the Earth’s surface using linear and angular measurements. The products are maps, plans, cross-sections, and control points for engineering or cadastral work.

Levelling is the part of surveying that finds relative heights (elevations) between points.

Two jobs are always linked:

• Surveying (data collection): measure what is on the ground.
• Laying out (setting out): put design points back onto the ground, such as building corners, road centre lines, or plot pegs.

2. Why we survey

• Village and cadastral maps showing boundaries, fields, and house sites
• Engineering plans for roads, canals, tanks, and buildings
• Topographic records of hills, streams, contours, and built features
• Control networks that provide a reliable framework for later surveys

3. Plane surveying vs geodetic surveying

Comparison	Plane surveying	Geodetic surveying
Earth curvature	Ignored; the working surface is treated as flat	Accounted for
Typical extent	Relatively small areas	Large networks and long distances
Angles and distances	Plane geometry	Spherical or ellipsoidal geometry
AP day-to-day use	Most village, mandal cadastral, and local engineering surveys	High-order control and large regional frameworks

4. Geoinformatics and reference surfaces

Geoinformatics combines surveying, positioning, remote sensing, GIS, and computing to collect, manage, analyse, and present location-based information. A coordinate is useful only when its reference system is known.

4.1 Reference systems for geoinformation

• Geoid: an irregular, gravity-based equipotential surface close to mean sea level.
• Ellipsoid: a smooth mathematical Earth model used for latitude, longitude, and ellipsoidal height.
• Datum: the definition that relates coordinates to an ellipsoid and the Earth.
• Projection: a method for representing curved Earth coordinates on a flat map or grid.

Geoid–ellipsoid separation (N) relates orthometric height from levelling to ellipsoidal height from GNSS. For chain survey of a village field you mostly work in a local plane; for GNSS or CORS work you must record the datum, projection, and units.

5. Two fundamental principles

5.1 Work from whole to part

Establish accurate control first—the outer framework—then fill in detail with simpler methods. This limits the spread of errors instead of allowing them to accumulate across the entire survey.

5.2 Fix a new point by at least two measurements

From known points A and B, locate a new point C by an independent combination such as:

• one distance and one angle;
• two distances by intersection; or
• chainage and a perpendicular offset from a known line.

6. How surveys are classified

6.1 By instrument

Survey type	Main idea
Chain survey	Linear measurements with detail fixed by offsets from chain lines
Compass survey	Bearings and measured line lengths form a traverse
Plane table	The map is drawn in the field while observations are made
Theodolite or total station	Precise angles, with electronic distance measurement on a total station
Levelling	Height differences measured with a level and staff
GPS or GNSS	Satellite positioning, including differential, CORS, and RTK methods
Photogrammetry or remote sensing	Maps and measurements derived from images

6.2 By method

• Triangulation: a connected network of triangles whose angles are measured carefully.
• Traverse: connected open or closed lines with measured angles and lengths.

6.3 By purpose

• Cadastral: property and field boundaries
• Topographical: natural and built features
• Engineering: reconnaissance, design, setting out, and construction checks
• Specialised: geological, mine, hydrographic, military, and utility surveys

7. Land measurement tools and techniques

7.1 Units and conversions

• Linear SI units: metre and millimetre. Older records may use feet, links, or chains; convert values before combining systems. Use the unit converter to check practice calculations.
• Angular sexagesimal units: 1° = 60′ and 1′ = 60″. Other angular systems appear in specialised work.

7.2 Linear measurement instruments

Chains and tapes measure short field lengths directly. EDM and total stations measure distance electronically, while GNSS can establish longer baselines or coordinates when the observation method and reference system are controlled.

7.3 Angular measurement instruments

A compass measures magnetic bearings; a theodolite or total station measures horizontal and vertical angles; and a clinometer measures slope or vertical angle for less precise work. Instrument condition, centring, levelling, and observation checks matter as much as the reading.

8. Stages of a survey operation

1. Reconnaissance: understand the purpose, inspect the site and records, and choose stations and control.
2. Field observations: measure distances, angles, levels, coordinates, and detail with repeat or closure checks.
3. Field record: enter observations, sketches, station descriptions, units, date, and instrument details as primary evidence.
4. Office work: reduce and adjust observations, plot plans, calculate areas or volumes, and document checks.
5. Setting out or delivery: transfer approved points to the ground or issue the required plan, record, or report.

9. Scales on plans and maps

• Representative fraction (RF) = map distance divided by ground distance in the same units.
• A large scale such as 1:1000 shows more detail and is suited to layouts or field plans.
• A smaller scale shows a wider area with less detail.
• Write the scale on the sheet and avoid measuring from a print that has been resized unless a scale bar or known dimension is available.

10. Continue learning

• Chain survey instruments
• Principles of cadastral survey in AP
• Diagonal and offset (D&O) system
• Online survey tools for area, FMB, units, and GIS