The instrument you pick decides what you can measure. A chain gives you distances but no angles. A theodolite gives you precise angles. A tacheometer gives you distance, angle and height together. Each instrument therefore defines its own kind of survey.
This post covers all eight types, and — more usefully — how they rank against one another for accuracy.
The Eight Types
- Chain surveying
- Compass surveying
- Levelling
- Plane table surveys
- Theodolite surveys
- Tacheometric surveys
- Photogrammetric surveys
- EDM surveys
1. Chain Surveying
The simplest type of surveying, in which only linear measurements are taken, either with a chain or a tape.
Angular measurements are not taken in chain surveying.
That note is the defining fact and the most examined one. Chain surveying gives you distances only — no angles at all. Positions are fixed purely by measuring lengths from known points, which is why chain surveys rely on triangles: a triangle is the only shape whose form is fully determined by its side lengths alone.
2. Compass Surveying
- Horizontal angles are measured with a magnetic compass, in addition to linear measurements taken with a chain or tape.
- A magnetic compass is not a precise angle-measuring instrument, so compass survey is not very accurate.
- However, it is more accurate than a chain survey.
Note the careful ranking here — compass surveying is imprecise in absolute terms, but better than chain surveying. Adding even a rough angular measurement to linear measurement improves the result, because it removes the need to build everything from triangles alone.
3. Levelling
A levelling instrument is used for determination of relative elevations (levels) of various points in the vertical plane.
This is the only one of the eight concerned with the vertical plane. Every other type in this list works horizontally. Levelling supplies the height information that plans and maps show as spot heights or contours.
4. Plane Table Surveys
A map or plan is prepared in the field while viewing the terrain, after determining the directions of various lines and measuring linear distances with a chain or tape.
| Accuracy | Main Advantage |
|---|---|
| Low | Measurements and plotting are done simultaneously in the field |
The trade-off here is unusually clear. Plane tabling sacrifices accuracy for a genuine practical benefit — the drawing is finished before you leave site. Since the surveyor is looking at the actual terrain while plotting, nothing gets forgotten or misinterpreted back in the office. There is no separate plotting stage at which errors can creep in.
5. Theodolite Surveys
- Horizontal and vertical angles are measured with a theodolite.
- A theodolite is a very precise instrument for measuring horizontal and vertical angles.
Theodolite surveys are quite accurate.
Two Types of Theodolite Survey
| Traverse Survey | Triangulation Survey | |
|---|---|---|
| Shape formed | Stations form a polygon | Lines form a system of triangles |
| Angles | Measured with theodolite | Measured, then used for computation |
| Lengths | Measured with a tape | Computed from measured angles, after accurately measuring one base line |
| Used for | General survey work | Establishing control points over extensive areas |
The Key Difference
In a traverse, you measure both angles and lengths for every line.
In triangulation, you measure only one length — the base line — with great accuracy, and then compute every other length from the measured angles.
Why go to that trouble? Because measuring long distances accurately across rough country is extremely difficult, while measuring angles is comparatively easy. Triangulation therefore minimises the hard work: measure one baseline carefully, then let trigonometry do the rest. This is exactly why it is used for control points over extensive areas, and why it underpins geodetic surveying.
6. Tacheometric Surveys
- A special type of theodolite called a tacheometer is used.
- It is fitted with a stadia diaphragm having two horizontal cross hairs in addition to the central horizontal hair.
- Horizontal angles, horizontal distances and vertical distances (elevation) are all measured with the tacheometer.
Tacheometric surveys are not very accurate in plane areas, but are extremely convenient and give better results than theodolite surveys in rough terrain.
Why Rough Terrain Reverses the Ranking
This is the most interesting statement in the whole topic, and it deserves explanation.
A theodolite survey needs lengths measured with a tape. On flat, open ground that is straightforward and very accurate. On steep, broken or vegetated ground it becomes slow and error-prone — the tape sags, cannot be held horizontal, and may not reach across obstacles at all.
A tacheometer measures distance optically, using the stadia hairs and a staff. It never touches the ground between the instrument and the point. So in terrain where taping is difficult, the tacheometer’s modest inherent accuracy beats the theodolite’s theoretically better accuracy that cannot be achieved in practice.
The lesson: the most accurate instrument is the one that works in the conditions you actually have.
7. Photogrammetric Surveys
Photogrammetry is the science of taking measurements with the help of photographs.
- Generally used for topographic mapping of large areas.
- Extremely useful for obtaining topographical details of areas which are difficult to access.
- Photographs are generally taken from an aeroplane; where suitable sites exist, they can also be taken from ground-based cameras.
The great advantage is that you do not have to go there. A dense forest, a marsh, a mountainside or a war zone can be mapped from the air. It is also fast — one flight captures what would take field parties months.
8. EDM Surveys
The instrument here is the Electronic Distance Measurement device, and it enables trilateration.
Trilateration is a type of triangulation in which all three sides of each triangle are measured accurately with the help of EDM instruments. The angles are then computed indirectly from the known sides. Hence all the sides and angles are determined.
Triangulation versus Trilateration
| Triangulation | Trilateration | |
|---|---|---|
| Measured | Angles, plus one base line | All three sides |
| Computed | All other lengths | All angles |
| Instrument | Theodolite | EDM |
The two are exact opposites. Triangulation measures angles and computes lengths; trilateration measures lengths and computes angles.
The reversal happened because of technology. Before EDM, measuring long distances accurately was the hard part, so triangulation avoided it. Once EDM made distance measurement fast and precise, that constraint disappeared — and it became easier to measure all three sides than to measure angles.
Accuracy Ranking
Pulling together every accuracy statement in this topic:
| Survey Type | Accuracy as Stated |
|---|---|
| Plane table | Low |
| Chain | Simplest; less accurate than compass |
| Compass | Not very accurate, but more accurate than chain |
| Tacheometric | Not very accurate in plane areas; better than theodolite in rough terrain |
| Theodolite | Quite accurate |
Two comparative statements are directly examinable and should be memorised as written: compass is more accurate than chain, and tacheometric beats theodolite in rough terrain.
What Each Instrument Measures
| Survey | Linear | Horizontal Angle | Vertical / Elevation |
|---|---|---|---|
| Chain | Yes | No | No |
| Compass | Yes | Yes (magnetic) | No |
| Levelling | — | — | Yes |
| Theodolite | Yes (tape) | Yes (precise) | Yes (angles) |
| Tacheometric | Yes (optically) | Yes | Yes |
| EDM | Yes (electronically) | Computed | — |
Quick Revision Notes
- Eight types: chain, compass, levelling, plane table, theodolite, tacheometric, photogrammetric, EDM.
- Chain surveying is the simplest; only linear measurements; no angular measurements at all.
- Compass measures horizontal angles magnetically; not very accurate but more accurate than chain.
- Levelling determines relative elevations in the vertical plane.
- Plane table: accuracy is low; main advantage is that measurement and plotting happen simultaneously in the field.
- Theodolite measures horizontal and vertical angles precisely; theodolite surveys are quite accurate.
- Traverse: stations form a polygon, angles by theodolite, lengths by tape.
- Triangulation: lines form triangles, base line measured accurately, all other lengths computed from angles; used for control points over extensive areas.
- Tacheometer is a theodolite with a stadia diaphragm having two extra horizontal cross hairs; measures horizontal angles, horizontal distances and elevations.
- Tacheometric surveys give better results than theodolite surveys in rough terrain.
- Photogrammetry is measurement from photographs, used for topographic mapping of large or inaccessible areas; photographs usually from aeroplanes.
- Trilateration measures all three sides with EDM and computes the angles.
Mistakes Students Commonly Make
- Saying chain surveying measures angles. It takes only linear measurements.
- Ranking chain above compass. Compass is more accurate than chain.
- Confusing traverse and triangulation. Traverse forms a polygon with measured lengths; triangulation forms triangles with computed lengths.
- Saying triangulation measures all sides. It measures one base line and computes the rest.
- Reversing trilateration. It measures all three sides and computes the angles — the opposite of triangulation.
- Assuming theodolite surveys are always best. In rough terrain, tacheometric surveys give better results.
- Forgetting that the tacheometer’s stadia diaphragm has two horizontal cross hairs in addition to the central one.
- Overlooking that plane tabling’s low accuracy is offset by simultaneous measurement and plotting.
Conclusion
Each instrument defines its own survey. The chain gives lengths alone, the compass adds rough angles, the level supplies heights, the plane table trades accuracy for finishing the plot on site, the theodolite gives precise angles, the tacheometer measures distance optically and wins in rough ground, photogrammetry maps places you cannot reach, and EDM turns triangulation on its head by measuring all three sides. Learn the two comparative statements — compass beats chain, and tacheometric beats theodolite in rough terrain — and the accuracy questions look after themselves.
Frequently Asked Questions
What is chain surveying?
The simplest type of surveying, in which only linear measurements are taken with a chain or tape. No angular measurements are taken.
Is compass surveying more accurate than chain surveying?
Yes. A magnetic compass is not a precise angle-measuring instrument, so compass surveying is not very accurate, but it is more accurate than chain surveying.
What is levelling used for?
Determination of the relative elevations, or levels, of various points in the vertical plane.
What is the main advantage of plane table surveying?
That measurements and plotting are done simultaneously in the field, while the surveyor is viewing the actual terrain. Its accuracy, however, is low.
What are the two types of theodolite survey?
Traverse survey, in which the stations form a polygon, and triangulation survey, in which the lines form a system of triangles.
How does triangulation differ from traverse?
In a traverse, angles are measured with a theodolite and lengths with a tape. In triangulation, only the base line is measured accurately and all other lengths are computed from the measured angles.
What is a tacheometer?
A special type of theodolite fitted with a stadia diaphragm having two horizontal cross hairs in addition to the central horizontal hair, used to measure horizontal angles, horizontal distances and elevations.
Why are tacheometric surveys better in rough terrain?
Because the tacheometer measures distance optically rather than by taping. In rough ground, taping becomes slow and error-prone, so the tacheometer outperforms the theodolite despite being less accurate on flat ground.
What is photogrammetry?
The science of taking measurements with the help of photographs, generally used for topographic mapping of large areas and for obtaining details of areas that are difficult to access.
What is trilateration?
A type of triangulation in which all three sides of each triangle are measured accurately using EDM instruments, and the angles are then computed indirectly from the known sides.