Scale Drawing
Part of Surveying
How to create accurate reduced-scale drawings of buildings, land parcels, and terrain from field measurements.
Why This Matters
A scale drawing is a map or plan where all distances are reduced by a consistent ratio — the scale. A drawing at 1:100 scale is one-hundredth of the size of the real thing, but every measurement on the drawing is proportionally correct. Scale drawings allow you to represent a 50-meter field on a piece of paper 50 centimeters across, and to read dimensions back off the drawing with confidence.
Scale drawings are essential for planning, communication, and construction. A building cannot be designed in words alone — the relationships between spaces, the positions of doors and windows, the structural requirements all become clear only when drawn to scale. A community cannot plan its land use from a verbal description — the actual pattern of fields, roads, water features, and buildings must be visible simultaneously. A drainage system cannot be designed without seeing the watershed as a whole.
The skill of making accurate scale drawings is accessible to anyone who can measure carefully and draw with a straight line. The drawings do not need to be artistic — they need to be accurate. A plain, precise drawing is more valuable than a beautiful but inaccurate one.
Scale Fundamentals
Representative fraction: Scale is expressed as a ratio or fraction. A scale of 1:500 means one unit on paper equals 500 units on the ground. The unit can be centimeters, millimeters, or any consistent unit.
Map distance from ground distance: Map distance = Ground distance / Scale denominator At 1:500: A 75 m wall = 7500 cm on the ground = 7500 / 500 = 15 cm on the map.
Ground distance from map distance: Ground distance = Map distance × Scale denominator At 1:200: A 6.5 cm line on the map = 6.5 × 200 = 1300 cm = 13 m on the ground.
Choosing an appropriate scale:
| Drawing Type | Typical Scale | Sheet Covers |
|---|---|---|
| Building floor plan | 1:50 or 1:100 | A room to a house |
| Site plan (single property) | 1:200 or 1:500 | A house and yard |
| Farm plan | 1:1000 or 1:2000 | A farm |
| Village plan | 1:5000 | A small settlement |
| Regional map | 1:25000 or smaller | Many kilometers |
Choose a scale that fits your subject on a manageable sheet of paper while keeping the drawing large enough to add dimensions and notes clearly. A drawing crowded with tiny numbers is worse than a larger drawing with clear annotations.
Making a Scale Ruler
A scale ruler has distance marks at the paper scale, allowing you to measure directly without converting. To make one:
- Take a straight strip of material about 30 cm long (wood, bone, stiff hide).
- Choose your working scale (e.g., 1:500).
- At this scale, 1 meter on the ground = 0.2 cm on paper. Mark 0.2 cm intervals along the ruler, labeled 0, 1, 2, 3… in meters.
- Extend subdivisions: divide the first meter into 10 parts for reading to 10 cm increments.
- Mark the scale prominently: “Scale 1:500” or “1 cm = 5 m.”
If you work at multiple scales regularly, make a separate ruler for each scale. Using the wrong scale ruler is a common and potentially serious drafting error — color-code them.
Setting Up a Drawing
Paper preparation: Use the largest smooth paper available. Tape or pin the paper flat to a drawing board (a smooth, flat surface). Ensure the paper will not shift during drawing.
Establishing orientation: Draw a north arrow first. Orient the drawing so north is near the top of the sheet (standard map orientation). If a different orientation makes better use of the sheet or aligns better with the subject, a different orientation is acceptable but the north arrow becomes even more important.
Border and title block: Draw a border line 1-2 cm inside the paper edge on all sides. In the lower right corner, reserve space for the title block:
- Drawing title
- Location or project name
- Scale (both as fraction and graphical bar)
- Date
- Drawn by (name)
- Sheet number
Grid: For large or complex drawings, draw a light grid at convenient intervals (1 cm or 2 cm) across the sheet. The grid provides a reference for maintaining consistent scale and allows another person to check dimensions by counting grid squares.
Drawing Techniques for Accuracy
Straight lines: Use a straightedge (ruler or flat board) and a consistent pencil pressure. Vary the pressure at the start and end of a line to avoid overshots. Long lines in one stroke are more accurate than multiple overlapping strokes.
Parallel lines: After drawing one line, place the straightedge against it, then slide it sideways to the required distance and draw the parallel line. Alternatively, mark two points at the required perpendicular distance from the original line and connect them.
Perpendicular lines: The 3-4-5 triangle method works on paper just as in the field. Mark a point 3 units along one line, 4 units along the perpendicular direction (approximate), then check that the diagonal is exactly 5 units. Adjust until it is, then draw the perpendicular.
Circles and arcs: Use a compass (two-legged divider with a pencil at one end). Set the radius carefully against your scale ruler before drawing. For large-radius curves, use a beam compass (a bar with adjustable point and pencil holders). A string tied to a fixed pin also makes a circle.
Angles: Use a protractor to lay off angles. Place the protractor center at the vertex of the angle, align the base line with one side, and mark the required angle. Connect the vertex to the mark with a straightedge.
Inking: Once a pencil draft is complete and checked, ink over the important lines for permanence. Work from top to bottom and left to right to avoid smearing fresh ink. Let each section dry before covering with your hand or straightedge. Erase pencil lines only after the ink is fully dry.
Common Drawing Types
Site plan: Shows a building and its immediate surroundings — fences, paths, trees, wells, outbuildings. Includes dimensions, orientation, and scale. Essential before any construction for planning space use and identifying conflicts.
Floor plan: A horizontal cross-section through the building at about 1 meter height, showing wall thicknesses, door and window openings, room dimensions, and structural elements. The primary design document for any building.
Profile (section) drawing: A vertical cross-section through a structure or terrain feature. Shows what you would see if you cut straight through the subject and looked at the cut face. Essential for showing foundation depths, roof pitches, stair geometry, and terrain profiles.
Survey plat: A precise map of a land parcel, showing boundaries, dimensions, areas, corner monument descriptions, and bearings. The legal record of a property’s extent and location.
Contour map: Shows elevation through a system of contour lines. Can be drawn from a grid of surveyed elevations or from a profile and cross-section survey.
Checking a Finished Drawing
Before using a finished drawing, verify it against the original field data:
- Measure at least five distances on the drawing with a scale ruler and compare to the field measurements. Discrepancies over 1% indicate a scaling error.
- Verify that closed polygons close: in a building floor plan, all the rooms should fit together without gaps or overlaps. In a land parcel map, the last boundary line should return exactly to the starting point.
- Verify right angles: corners that should be 90° should look 90° in the drawing. Use a set square to check.
- Have someone else check the drawing against the field notes — a second pair of eyes catches errors the drafter misses.
Revision marking: If a drawing is revised after its first use, mark all revised areas clearly (“REVISED [date]”). Never revise a drawing so that the original is obliterated — someone may need to see what was originally drawn. If the revision is major, make a new drawing and mark the old one “SUPERSEDED.”
Graphical Scale Over Text Scale
Always include a graphical scale bar on every drawing. A text scale (“Scale 1:500”) loses meaning if the drawing is reduced or enlarged in reproduction. A graphical bar scales with the drawing and is always correct. Without it, a photocopied or traced drawing has no recoverable scale.