Site Information, Survey Drawings and Setting Out

Introduction

A building is constructed on land that already has a physical form, legal identity and measurable position. Before a designer prepares a site plan or a contractor begins excavation, the existing site must be understood accurately. Site information includes the shape and dimensions of the allotment, legal boundaries, access, services, vegetation, adjoining buildings, ground levels, drainage patterns and restrictions such as easements. Survey drawings communicate this information in a controlled graphical form.

For a civil draftsman, the ability to interpret and prepare survey-based drawings is fundamental. A drawing that places a building only a few hundred millimetres beyond a boundary, misrepresents a contour, or uses an incorrect benchmark can cause construction delays, disputes, drainage failure and expensive rectification. CAD improves speed and presentation, but it does not remove the need for surveying principles, checking and professional judgement.

This chapter explains how to read survey plans, use contours and levels, interpret coordinates and boundaries, prepare site and grading information, and develop a basic setting-out drawing.

Learning objectives

On completing this chapter, a student should be able to:

• identify the principal components of a survey plan;
• distinguish cadastral, topographic and construction information;
• interpret boundaries, easements, services, benchmarks and survey symbols;
• calculate and check reduced levels, gradients, distances and coordinates;
• read contours and infer drainage behaviour;
• prepare a clear site plan and basic grading plan in CAD;
• convert design dimensions and coordinates into setting-out information;
• apply appropriate checking, documentation and safety procedures; and
• recognise the limitations of survey data and the responsibilities of the draftsman.

1. The information base for site drawing

1.1 Surveying and the survey plan

Surveying is the measurement and representation of points, lines and surfaces on or near the Earth. A survey plan is not merely an illustration: it is a measured record prepared for a defined purpose and accuracy. The purpose may be cadastral definition, preliminary design, earthworks, drainage, construction or as-built documentation.

A drawing should state its purpose, survey date, surveyor or source, coordinate system, height datum, scale, north direction, units and relevant qualifications. Data from different surveys must not be combined casually. Two plans may use different datums, origins, accuracies or dates.

1.2 Types of site information

A cadastral boundary is a legal concept represented by survey evidence. A fence, hedge or wall may indicate occupation but is not automatically the legal boundary. The title, deposited plan and surveyor's interpretation take precedence.

1.3 Drawing conventions

Survey and site drawings commonly use a plan view with north indicated by an arrow. A title block should identify the project, drawing title, number, revision, scale, date, author, checker and status. The legend explains symbols for trees, pits, hydrants, poles, fences, kerbs, contours and services.

Line weight and line type communicate hierarchy. Existing features are often shown with lighter or dashed lines, while proposed works are shown more prominently. However, office and authority standards vary; the project standard must be followed rather than assumed.

A scale bar is valuable because drawings may be printed at a non-standard size. Numerical scale alone can become misleading after enlargement or reduction. Dimensions and coordinates should be used for construction; scaled measurements from a drawing are not a substitute for stated dimensions.

2. Coordinates, orientation and reference systems

2.1 Coordinate systems

A point may be described by rectangular coordinates such as eastings and northings, or by local axes such as X and Y. In a common surveying convention, easting increases to the east and northing increases to the north. A local project grid may instead define an arbitrary origin for convenience. The drawing must identify which system is used.

For two points A and B with coordinates (Eₐ, Nₐ) and (Eᵦ, Nᵦ), the coordinate differences are:

The horizontal distance is:

Here, ΔE and ΔN are coordinate differences and d is the horizontal distance; all must use the same unit, normally metres. This relationship assumes a rectilinear horizontal coordinate system and a distance sufficiently small for the adopted projection or local grid to be appropriate.

The direction angle can be calculated using a quadrant-aware arctangent:

When θ is measured clockwise from north, it is an azimuth. The function atan2 is preferred to a simple inverse tangent because it identifies the correct quadrant. CAD software may use a different angular convention, such as angles measured counter-clockwise from the positive X-axis. The drafter must confirm the software settings before transferring survey bearings.

Worked example 1: distance between control points

Point A has coordinates E = 1250.000 m, N = 860.000 m. Point B has coordinates E = 1286.000 m, N = 908.000 m.

ΔE = 1286.000 − 1250.000 = 36.000 m

ΔN = 908.000 − 860.000 = 48.000 m

The horizontal distance is therefore 60.000 m. The result is consistent with the 3–4–5 triangle scaled by 12.

2.2 Bearings and azimuths

A bearing describes direction relative to a meridian, commonly using quadrants such as N 35° E. An azimuth is usually a clockwise angle from north, ranging from 0° to less than 360°. A bearing must not be entered into CAD as an azimuth without conversion.

For example, N 35° E corresponds to an azimuth of 35°. S 20° E corresponds to 180° − 20° = 160°. N 15° W corresponds to 360° − 15° = 345°. The notation and conversion rule must be recorded on the drawing or survey computation sheet.

2.3 Grid north, true north and magnetic north

True north relates to the geographic meridian. Grid north relates to the map projection. Magnetic north relates to the Earth's magnetic field and varies with location and time. A site plan may show more than one north reference. For ordinary building set-out, the project grid or survey control system is normally the controlling reference, not an unqualified magnetic compass reading.

3. Levels, benchmarks and vertical datums

3.1 Reduced levels

A reduced level (RL) is the elevation of a point relative to an adopted vertical datum. The datum may be a national datum, a local benchmark or an assumed project datum. Every level on a drawing must be interpreted with its datum.

A benchmark (BM) is a point with a known or adopted RL. It may be a permanent monument, a survey mark, a kerb nail or a temporary site benchmark. A temporary benchmark should be protected and described clearly so that it can be re-established.

3.2 Height of instrument method

In differential levelling, the height of instrument (HI) is calculated by adding a backsight reading to the known RL:

The RL of an unknown point is then:

where BS is the backsight, FS is the foresight, and all quantities are in the same length unit. The method assumes the staff readings are taken with a correctly levelled instrument and that the line of sight and instrument setup are properly controlled.

Worked example 2: transferring a benchmark

A benchmark has RL 102.450 m. A backsight of 1.325 m is taken, followed by a foresight of 2.080 m to point P.

Point P is therefore 101.695 m relative to the stated datum. A check should be made by closing the levelling run on a known benchmark or by an independent observation.

3.3 Level arithmetic checks

For a levelling run, the arithmetic check is:

The equation checks arithmetic consistency; it does not prove that the field observations are free from systematic or blunder errors. A closure error must be assessed against the applicable survey tolerance. A draftsman should never silently alter levels to make a drawing appear consistent.

4. Contours and ground form

A contour is a line joining points of equal elevation. The contour interval is the vertical difference between successive contours, such as 0.5 m or 1.0 m. Contours are interpolated from surveyed points or generated from a terrain model, so their accuracy depends on point density, observation quality and interpolation method.

Important interpretation rules are:

• contours generally do not cross, except where unusual terrain such as an overhang is represented;
• close contours indicate a steep slope;
• widely spaced contours indicate a flatter slope;
• contours form a V pointing uphill where they cross a drainage line;
• a ridge produces V or U shapes pointing downhill; and
• closed contours may represent a hill or depression, which should be identified from spot levels or depression symbols.

The approximate slope between two points is:

where s is slope as a decimal ratio, Δh is the vertical change and L is the horizontal distance. Percentage slope is:

For a fall, Δh is commonly taken as the positive magnitude of the level difference and the direction is stated separately. If point A has RL 101.20 m, point B has RL 100.40 m, and the horizontal distance is 40 m, the fall is 0.80 m and the slope is 0.80/40 = 0.020, or 2.0% (1 in 50).

Slope notation must be used carefully. “1 in 50” means one unit of vertical change for 50 units horizontally. It is not 50%. The equivalent percentage is 100/50 = 2%.

Figure: Typical site-plan relationship between contours, a proposed building and a benchmark.

Contours alone do not provide a complete construction model. Spot levels are needed at corners, thresholds, kerbs, pits, ridges, low points and other critical locations. A draftsman should preserve surveyed spot levels and distinguish them from proposed design levels.

5. Boundaries, easements and site constraints

5.1 Boundaries and setbacks

A site plan should show the legal lot boundary, boundary dimensions, adjoining lots or roads, and relevant title information. Setbacks are measured from the legally established boundary or another specified reference, not automatically from a fence. Building envelopes may also be controlled by planning regulations, fire separation, access requirements, overlooking controls or heritage restrictions.

Dimensions should be arranged so that they do not obscure the boundary or building. Redundant dimensions can create contradictions. A dimension chain should be checked: partial dimensions should add to the stated overall dimension, allowing for any stated rounding.

5.2 Easements and covenants

An easement is a legal right benefiting one party over land owned or controlled by another, commonly for drainage, sewerage, access or services. An easement may restrict building, excavation, planting or access. Its width, alignment and registered instrument must be identified from authoritative title information.

A covenant, restriction or planning designation may impose additional requirements. The draftsman should show the relevant notation and refer the issue to the surveyor, architect, engineer, planner or legal authority. A graphic line on a drawing does not itself create or remove a legal right.

5.3 Services and existing features

Underground services include water, sewer, stormwater, electricity, gas, telecommunications and irrigation. Service records may be approximate, incomplete or outdated. Before excavation, the responsible contractor must use the applicable locating and permit procedures. A CAD layer labelled “service” is not proof of exact physical location.

Existing trees, retaining walls, poles, kerbs, driveways, fences and adjoining buildings should be surveyed where they influence design or construction. Tree protection zones and root zones may be regulatory constraints. The drawing should distinguish observed, supplied and assumed information.

6. Preparing a site plan in CAD

A reliable CAD workflow is as important as drafting speed.

Step 1: establish the project basis

Collect the survey file, title plan, coordinate and vertical datum information, field notes, design brief and applicable standards. Confirm units, origin, north direction and whether the survey is in a projected or local grid.

Step 2: create a disciplined layer structure

A practical layer structure may include:

Layer names, colours and lineweights should comply with the office or project CAD standard. Colours should not be the only means of distinguishing information because drawings may be printed monochrome or viewed by colour-impaired users.

Step 3: import and verify survey data

Use a controlled insertion method. Check a known coordinate, a known distance, a benchmark and the orientation of north. Never “fit” a survey visually to an architectural drawing without recording the transformation and obtaining approval.

Step 4: draft existing conditions

Draw the boundary, title dimensions, contours, spot levels, structures, access, services and significant vegetation. Use labels that remain legible at the intended plotting scale. Avoid copying unexplained objects from a source file; inspect their layers, units and blocks.

Step 5: add the proposed design

Show the building footprint, setbacks, finished floor level (FFL), external paving, driveways, retaining walls, ramps, drainage points and proposed levels. Label existing levels as “EX” and proposed levels as “PROP” or by the project convention.

Step 6: annotate and check

Include north arrow, scale bar, legend, datum, survey source, drawing status and notes. Check closure of dimensions, consistency of levels, accessible paths, drainage falls, boundary clearances and conflicts with easements or services. Plot a review copy and inspect it at actual paper size.

7. Grading and drainage information

Grading is the shaping of the ground to achieve drainage, access, stability and suitable building platforms. The design must coordinate finished floor levels, thresholds, paving, kerbs, pits, retaining walls and legal discharge points.

Water generally flows downslope, but local grading, walls and pits can redirect it. A grading plan should therefore show arrows indicating fall direction, proposed spot levels at changes in grade, longitudinal grades along paths and drainage structures. It should not rely solely on contours.

For a proposed line between two points, the level at an intermediate distance x along a uniform grade can be calculated by linear interpolation:

where RL_A and RL_B are endpoint levels, L is the horizontal length, and x is measured from A toward B. This assumes a straight uniform grade and a horizontal distance basis. It is not appropriate where a vertical curve or abrupt grade change is designed.

Worked example 3: proposed path grade

A path begins at RL 100.240 m and ends 12.0 m away at RL 99.880 m.

Fall = 100.240 − 99.880 = 0.360 m.

At 5.0 m from the start, assuming uniform grade:

The path falls 0.150 m over the first 5 m and has an interpolated level of 100.090 m. Accessibility, drainage and local regulations must still be checked; a mathematically correct grade may not meet all design requirements.

8. Setting-out drawings and construction control

Setting out transfers the position, alignment and levels shown in design documents to the physical site. A setting-out drawing is not normally a complete survey plan. It communicates the geometry that the contractor or surveyor must establish using reliable control.

8.1 Control points and working points

Control points are stable reference points with known horizontal coordinates and/or RLs. They should be outside the disturbance area where possible. Working points may be temporary marks used to set out walls, grid intersections or offsets.

A setting-out plan commonly includes:

• survey control points and coordinate schedule;
• building grid lines and grid labels;
• baseline or nominated axes;
• dimensions between grids and to boundaries;
• corner coordinates or set-out points;
• offsets to pegs or batter boards;
• finished floor and excavation levels;
• orientation and datum notes; and
• tolerances, revision status and surveyor instructions.

8.2 Baseline and offset method

A simple method establishes a baseline between known points, then locates building corners by measured offsets or coordinate calculations. Offsets should be taken from a line that remains accessible after excavation. Batter boards or profile boards preserve the alignment when trenches are dug.

For right-angle construction, diagonals provide an important check. For a rectangular building with side lengths a and b, the diagonal is:

Both diagonals should be equal in an ideal rectangle. Differences may arise from measurement tolerance, but a significant discrepancy indicates an error in dimensions, squareness or point identification.

8.3 Coordinate set-out

If a corner has design coordinates (E_d, N_d) and the surveyor observes a site point (E_o, N_o), the coordinate differences are:

The instrument or field controller converts these differences into a direction and distance according to its configuration. The draftsman must provide unambiguous coordinates, units, datum and point descriptions. A coordinate list without a defined reference system is incomplete.

8.4 Vertical set-out

Levels are transferred from a benchmark to establish excavation, footing, slab and finished floor levels. The drawing should identify whether a value is an RL, FFL, underside level, top-of-concrete level or another reference. “Level 0.000” has meaning only when its datum is stated.

9. Illustrative applied case: small sloping residential site

Background

This illustrative case concerns a 32 m by 20 m residential lot falling toward the street. The survey identifies a rear benchmark with RL 104.200 m, existing contours at 0.5 m intervals, a sewer easement along one side boundary and an existing driveway connection at the front.

Problem

The designer proposes a rectangular house, a garage entry from the street and a rear patio. The building must remain outside the easement, achieve a suitable finished floor level and drain paved areas without directing runoff onto the neighbouring property.

Analysis

The survey shows that the rear of the site is approximately 1.20 m higher than the front over a horizontal distance of 20 m. The average existing grade is therefore:

The contour pattern indicates that water moves toward the street, but a proposed retaining wall near the patio could create a low point. The easement prevents the house footprint from extending into the side strip, and service records indicate that the sewer alignment requires confirmation before excavation.

Approach and solution

The draftsman establishes the survey file in the supplied local coordinate system, verifies the front boundary length against the title plan and places the proposed house using grid coordinates rather than visual scaling. A finished floor level is selected after coordination with driveway and street levels. The grading plan shows:

• proposed FFL and slab edge levels;
• a fall away from the house toward collection points;
• spot levels at the patio, driveway and boundary;
• a retaining wall with top and bottom levels;
• drainage pits connected to the approved discharge system; and
• the sewer easement and a note requiring service location confirmation.

The setting-out plan uses two control points outside the excavation zone. Building grid intersections are dimensioned to the control line, and diagonals are listed as an independent squareness check.

Outcome

The coordinated drawings allow the surveyor to establish the building accurately, provide the contractor with usable levels and reveal the drainage and easement constraints before construction. The drawing set is issued with a revision cloud around the changed patio and a note identifying the survey source and datum.

Learning points

The case demonstrates that a site plan is an integrated technical document. Boundary information, topography, legal constraints, drainage and construction geometry must agree. CAD presentation cannot compensate for an unverified datum, uncertain service location or incorrectly interpreted boundary.

10. Quality assurance, safety and professional responsibility

Common errors include using the wrong units, rotating a survey incorrectly, confusing grid and magnetic north, omitting the vertical datum, scaling dimensions from a printed plan, labelling proposed levels as existing, and failing to update a revised survey. A formal check should be performed by someone other than the original drafter where project procedures require it.

A useful review sequence is:

1. confirm source, date, units and datums;
2. verify a known distance and coordinate;
3. check boundary dimensions and title references;
4. compare contours with spot levels;
5. check levels and grade arrows mathematically;
6. confirm easements, setbacks and service information;
7. inspect proposed geometry against control points;
8. review drawing scale, notes, legend and revision status; and
9. plot and visually inspect the issued PDF or sheet.

Safety is central to setting out. Excavation near services, unstable ground, traffic, plant and open trenches requires competent personnel and the applicable permits and controls. A drafter must not imply that an approximate service record is a safe excavation location. Surveyors and contractors must use current site procedures and authoritative utility information.

Ethically, the draftsman must distinguish fact, interpretation and assumption. Uncertain information should be qualified, not concealed. Copyright, privacy and security also matter: survey files may contain property information, service locations or personal data and should be distributed only to authorised project participants.

11. Digital surveying, BIM and emerging practice

Total stations, GNSS receivers, digital levels, terrestrial laser scanners, photogrammetry and unmanned aerial systems can produce dense point clouds and terrain models. CAD and BIM platforms can then represent existing ground, proposed surfaces and construction coordinates. These technologies improve data capture and coordination but can also create false confidence. A dense model is not necessarily accurate, and automated surface triangulation may bridge gaps or misinterpret vegetation and structures.

Point-cloud data should be checked against control points, survey metadata, tolerances and the intended use. Coordinate transformations must be documented. Machine-learning tools may classify terrain or detect drawing conflicts, but professional responsibility remains with the competent person who verifies the result. AI-generated labels, contours or dimensions should never be issued without source validation and independent checking.

Best-practice checklist

Before issuing a site, grading or setting-out drawing, confirm that:

• the survey source, date, scale, units and datums are stated;
• north orientation and coordinate system are unambiguous;
• boundaries are based on authoritative information;
• easements, setbacks and restrictions are shown;
• existing and proposed information are clearly distinguished;
• benchmarks and reduced levels are identified;
• contours agree reasonably with spot levels;
• slope calculations use consistent units and correct direction;
• control points, grids and offsets are usable in the field;
• dimensions are not being inferred from scaling;
• service information is appropriately qualified;
• revisions are recorded and superseded drawings withdrawn; and
• the final plotted document has been independently checked.

Chapter Summary

Site information provides the factual and legal foundation for building design and construction. Survey plans combine cadastral, topographic and engineering information, but each source has a defined purpose, datum and accuracy. Coordinates locate points horizontally; benchmarks and reduced levels locate them vertically. Distance, direction, level and grade calculations must use consistent units and clearly stated conventions.

Contours communicate ground form, while spot levels provide critical local information. Boundaries must be distinguished from fences and other occupation features, and easements or service corridors can significantly restrict design. A professional CAD workflow establishes units and datums, organises layers, verifies imported data, separates existing from proposed information and applies systematic checking.

Setting-out drawings convert approved design geometry into field-controllable grids, coordinates, offsets and levels. They depend on reliable control points and must state the coordinate and vertical reference systems. Digital survey technologies, CAD, BIM and AI-assisted tools can improve efficiency, but they do not replace field verification, competent judgement, safety procedures or ethical disclosure of uncertainty.

Key Terms

Survey plan: A measured graphical record of site, boundary or construction information.

Cadastral survey: Surveying concerned with legal land boundaries and interests.

Topographic survey: Survey describing terrain and existing physical features.

Coordinate system: A defined reference framework for locating points numerically.

Easting: Coordinate component generally increasing toward the east.

Northing: Coordinate component generally increasing toward the north.

Bearing: Direction expressed relative to a meridian, often in quadrant notation.

Azimuth: Direction expressed as a clockwise angle from north.

Reduced level (RL): Elevation relative to an adopted vertical datum.

Benchmark (BM): Point with a known or adopted reduced level.

Height of instrument (HI): Instrument line-of-sight elevation in levelling calculations.

Contour: Line joining points of equal elevation.

Contour interval: Vertical difference between adjacent contour values.

Easement: Legal right or restriction affecting the use of land.

Setback: Required distance between a boundary or reference line and a building.

Finished floor level (FFL): Design elevation of a finished floor surface.

Grading: Planned shaping of land to achieve drainage, access and stability.

Setting out: Transferring design positions and levels to the physical site.

Control point: Stable point with known horizontal and/or vertical position.

As-built survey: Survey recording the location and levels of completed work.

Review Questions

Short Answer Questions

1. What is the difference between a cadastral survey and a topographic survey?
2. Why must a benchmark be associated with a stated vertical datum?
3. What information is communicated by the spacing of contour lines?
4. Why should a fence not automatically be accepted as a legal boundary?
5. Identify four items commonly shown on a setting-out drawing.

Long Answer Questions

1. Explain a systematic CAD workflow for preparing a site plan from survey information.
2. Describe how coordinates, bearings, azimuths and north references affect the interpretation of a survey drawing.
3. Explain the height-of-instrument method and the importance of levelling arithmetic checks.
4. Discuss the role of easements, services and setbacks in positioning a proposed building.
5. Explain how a grading plan differs from a contour plan and why both existing and proposed levels are required.

Analytical / Application Questions

1. Points A and B have coordinates A (E 1500.000 m, N 920.000 m) and B (E 1532.000 m, N 956.000 m). Calculate the horizontal distance and explain one checking procedure before using the result for set-out.
2. A proposed path is 18 m long and falls from RL 101.360 m to RL 100.910 m. Calculate its percentage grade and determine the RL 7 m from the higher end, assuming a uniform grade. State one practical issue that must also be checked.
3. A building footprint conflicts with a mapped drainage easement, while the site fence appears to provide more available space. Analyse what information should be verified and explain why the footprint should not simply be moved to the fence line.

Multiple Choice Questions with Answers

Question 1

Which document primarily defines the legal position of a land boundary?

A. A cadastral survey or title plan

B. A contour plan

C. A drainage grading plan

D. A reflected ceiling plan

Correct Answer: A. A cadastral survey or title plan

Question 2

A benchmark has RL 105.250 m and a backsight of 1.450 m. What is the height of instrument?

A. 103.800 m

B. 104.800 m

C. 106.700 m

D. 107.250 m

Correct Answer: C. 106.700 m

Question 3

What do closely spaced contour lines generally indicate?

A. A flat surface

B. A steep slope

C. A legal boundary

D. A vertical datum

Correct Answer: B. A steep slope

Question 4

For points with ΔE = 12 m and ΔN = 16 m, what is the horizontal distance?

A. 4 m

B. 20 m

C. 28 m

D. 192 m

Correct Answer: B. 20 m

Question 5

An easement on a site plan should be treated as:

A. A decorative landscape line

B. A legal interest or restriction requiring verification

C. An assumed building grid

D. A contour interval

Correct Answer: B. A legal interest or restriction requiring verification

Question 6

A line falls 0.60 m over a horizontal distance of 30 m. What is its percentage grade?

A. 0.5%

B. 2.0%

C. 5.0%

D. 50%

Correct Answer: B. 2.0%

Question 7

Which item is most important when importing a survey into CAD?

A. Changing all layers to one colour

B. Checking units, coordinates, orientation and datum

C. Scaling the drawing until it visually matches

D. Deleting the source metadata

Correct Answer: B. Checking units, coordinates, orientation and datum

Question 8

What is the main purpose of a control point in setting out?

A. To provide a stable known reference for positions or levels

B. To show the location of every tree

C. To replace the legal title plan

D. To indicate the contour interval

Correct Answer: A. To provide a stable known reference for positions or levels

Question 9

A proposed path starts at RL 100.200 m and ends at RL 99.800 m over 10 m. Assuming a uniform grade, what is the RL 5 m from the start?

A. 99.600 m

B. 99.800 m

C. 100.000 m

D. 100.400 m

Correct Answer: C. 100.000 m

Question 10

Why should a draftsman distinguish surveyed information from assumptions?

A. To make the drawing more colourful

B. To prevent uncertain information being mistaken for verified site data

C. To eliminate the need for a surveyor

D. To avoid using dimensions

Correct Answer: B. To prevent uncertain information being mistaken for verified site data