Introduction to surveying

This page is a short primer — not a full textbook. It defines surveying, the two main divisions, how we measure, and the order of work you will see in the field and office. For AP cadastral procedure, use the guides hub and the toolkit calculators linked at the end.

1. What surveying is

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 (building corners, road centre lines, plot pegs).

2. Why we survey

• Village and cadastral maps (boundaries, fields, house sites)
• Engineering plans (roads, canals, tanks, buildings)
• Topography (hills, streams, contours)
• Control networks for later, less precise surveys

3. Plane surveying vs geodetic surveying

	Plane surveying	Geodetic surveying
Earth curvature	Ignored (surface treated as flat)	Accounted for
Typical extent	Relatively small areas (classically < ~250 km²)	Large networks and long distances
Angles / distances	Plane geometry	Spherical / ellipsoidal geometry
AP day-to-day work	Most village / mandal cadastral and engineering surveys	High-order control, large state frameworks

4. Reference surfaces (minimal)

• Geoid — equipotential surface close to mean sea level; gravity-based; irregular.
• Ellipsoid — smooth mathematical Earth model for coordinates (latitude, longitude, ellipsoidal height).
• Geoid–ellipsoid separation (N) relates orthometric (spirit-level) height to ellipsoidal height.

For chain survey of a village field you mostly work in a local plane with chain and offset. For GNSS / CORS work you must know which datum and projection you are using.

5. Two fundamental principles

5.1 Work from whole to part

Establish accurate control first (outer framework), then fill detail with simpler methods. Errors stay inside the control net instead of growing across the whole survey.

5.2 Fix a new point by at least two measurements

From known points A and B, locate C by one of:

• Distance + angle
• Two distances (intersection)
• Perpendicular offset from a line (chainage + offset)

6. How surveys are classified

6.1 By instrument (common set)

Survey type	Main idea
Chain survey	Linear measurements; detail by offsets from chain lines
Compass survey	Bearings + chain lengths (traverse)
Plane table	Map drawn in the field while observing
Theodolite / total station	Precise angles (and EDM distances on total station)
Levelling	Height differences with level + staff
GPS / GNSS	Absolute / differential satellite positions (CORS, RTK)
Photogrammetry / remote sensing	Maps and measurements from images

6.2 By method

• Triangulation — network of triangles; angles measured carefully
• Traverse — connected lines (open or closed) with angles and lengths

6.3 By object (examples)

• Cadastral — property and field boundaries
• Topographical — natural and cultural features
• Engineering — design and construction of works (recon → preliminary → location)
• Geological, mine, military, city utility surveys, etc.

7. Units (linear and angular)

• Linear (SI): metre, millimetre. Older records may use feet, links, or chains — convert before mixing systems. Use the unit converter.
• Angular (sexagesimal): 1° = 60′, 1′ = 60″. Centesimal grads and time measures appear in specialised work.

Measurement	Typical instruments
Linear	Chain, tape, EDM, total station, GPS baselines
Angular	Compass, theodolite, total station, clinometer

8. Stages of a survey job

1. Field work
   • Reconnaissance — choose stations and control
   • Observations — distances, angles, levels, detail
   • Field record — field book / digital log (primary evidence)
2. Office work — reduce data, adjust small errors, plot plans, compute areas/volumes
3. Care of instruments — protect from sun/rain, clean optics, use cases for transport, never leave instruments unguarded on roads

9. Scales (plans and maps)

• RF (representative fraction) = map distance / ground distance (same units).
• Large scale (e.g. 1:1000) → more detail for layouts and FMB-style plans.
• Small scale → overview maps. Always write the scale on the sheet.

10. Next steps on this site

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