Producing accurate and precise plane geometry drawings is fundamental for architects in Kenya, as these drawings form the basis of architectural design, communication, and construction documentation. Mastery of line drafting techniques and the division of lines and circles into equal parts ensures that architectural plans and details are clear, standardized, and compliant with professional drafting conventions. This chapter equips students with essential skills to create geometrically accurate drawings that meet Kenya’s architectural industry standards and facilitate effective project execution.

1.1 Drawing lines drafting

In architectural drafting, lines are the primary means of representing objects, boundaries, and spatial relationships on a plane. Understanding the types of lines, their uses, and correct drawing methods is crucial for producing clear, professional architectural drawings that comply with BS 8888 and ISO 128 standards adopted in Kenya’s architectural practice. Accurate line drafting improves readability and minimizes misinterpretation in architectural plans, elevations, and sections.

1.1.1 Types of lines

Different types of lines convey specific information in architectural drawings, and each must be drawn with appropriate thickness and style for clarity and standardization.

1.1.1.1 Outline

• Continuous Thick Lines: These lines are used to represent visible edges and outlines in architectural drawings. They provide the primary shape and form of objects such as walls, doors, and windows.

An outline, also called a visible or object line, is a continuous thick line that shows the edges and boundaries of an object that can be seen in the view being drawn. Because it is the heaviest line on the drawing, it defines the main shape of the building and makes it stand out from dimensions, notes and other lighter lines. In plans and sections, the outline is also used for walls and elements cut through by the section plane. Example: on the ground floor plan of a health centre, all external and internal walls were drawn with thick outlines so that the room layout was clear at a glance.

Uses of Outlines

• Building perimeter: Showing the external boundary of the building in plans and elevations.
• Cut walls and floors: Showing elements cut by the section plane in plans and sections.
• Visible edges: Showing edges of doors, windows, steps and roofs visible in the view.
• Profile of elevations: Defining the silhouette of the building against the ground and sky.
• Ground line: Showing the finished ground level in elevations and sections.

Steps for Drawing Outlines

1. Set out lightly: Draw the shape first with light construction lines.
2. Check dimensions: Confirm all lengths and positions before darkening.
3. Choose the tool: Use a soft pencil or a thick technical pen for the outline.
4. Draw with steady pressure: Use the T-square and set squares to keep lines straight and uniform.
5. Join corners cleanly: Make lines meet exactly at corners without overshooting.
6. Check for consistency: Make sure all outlines have the same thickness and darkness.

1.1.1.2 Break line

• Break Lines: Indicate that a part of the drawing is omitted for clarity or to show a partial view, often used in long walls or repetitive elements.

A break line shows that part of an object has been cut away or left out of the drawing, either to save space or to show only the part that matters. It allows long elements such as walls, beams, pipes or railings to be drawn shorter than their true length, or allows an interior part to be revealed. There are two common forms: a long break line, drawn as a thin ruled line with zigzags, and a short break line, drawn as a thick freehand wavy line. Example: in a detail drawing of a long boundary wall for a primary school, the drafter used a zigzag break line to show only the two ends of the wall and the gate opening, saving space on the sheet.

Types of Break Lines

Guidelines for Drawing Break Lines

• Use the correct type: Choose long, short or cylindrical breaks to suit the element.
• Keep dimensions true: Dimension the full true length even though the drawing is shortened.
• Place breaks where nothing important is lost: Avoid breaking through openings or key details.
• Draw both sides consistently: The two ends of a break must line up with each other.
• Keep zigzags small and neat: Large, uneven zigzags distract from the drawing.

1.1.1.3 Centre line

• Chain Lines: Used to indicate centerlines or axes of symmetry in objects, important for aligning architectural elements.

A centre line is a thin chain line made of alternating long and short dashes, used to mark the centre of circles, arcs, symmetrical objects and the axes of walls, columns and grids. Centre lines help the builder set out elements accurately on site, since many dimensions are measured from them, and they show where an object is symmetrical so it does not need to be fully drawn on both sides. Typical proportions are long dashes of about 12 mm to 24 mm, gaps of about 1 mm to 3 mm and short dashes of about 1 mm to 2 mm, adjusted to the size of the drawing. Example: on the structural grid plan of a hotel block, every column grid line was drawn as a centre line and labelled A, B, C and 1, 2, 3, so the contractor could set out columns accurately.

Uses of Centre Lines

• Centres of circles and arcs: Two crossing centre lines mark the centre of round features such as columns and openings.
• Axes of symmetry: Show the line about which a symmetrical object is mirrored.
• Structural grids: Mark column and wall grid lines in plans.
• Paths of motion: Show the path of moving parts, such as a sliding door track.
• Setting-out lines: Mark reference lines for dimensioning and positioning elements.

Guidelines for Drawing Centre Lines

• Start and end with a long dash: Centre lines should not begin or end with a short dash or gap.
• Cross at long dashes: Where two centre lines cross, they should cross at the long dashes.
• Extend slightly beyond the object: Let centre lines project a few millimetres past the outline.
• Keep dash pattern uniform: Use the same dash and gap lengths throughout the drawing.
• Use thin lines: Centre lines must never be heavier than outlines.

1.1.1.4 Projection line

• Continuous Thin Lines: Utilized for dimension lines, projection lines, hatching, and detail lines. These lines highlight measurements and minor details without overpowering the main outlines.

A projection line, also called an extension line, is a thin continuous line that extends from a point or edge of an object to show where a dimension starts or ends, or to carry a point from one view to another. In dimensioning, projection lines run at right angles to the dimension line, so measurements can be placed clear of the object itself; in orthographic projection, they transfer heights and widths from plan to elevation. A small gap of about 1 mm to 2 mm is left between the object and the start of the projection line, and the line extends about 2 mm to 3 mm beyond the dimension line. Example: when preparing elevations of a bank branch, the drafter projected window positions from the plan up to the elevation using light projection lines, ensuring the two views matched exactly.

Uses of Projection Lines

• Dimensioning: Mark the limits of dimensions outside the outline of the object.
• Transferring points between views: Carry positions from plan to elevation or section.
• Showing alignment: Show that elements in different views line up.
• Extending features: Extend surfaces or edges to locate intersection points.
• Setting out from reference points: Project from grid lines or datums to positions on the drawing.

Steps for Drawing Projection Lines for a Dimension

1. Identify the points to dimension: Choose the two edges or points the dimension will measure between.
2. Leave a small gap: Start each projection line about 1 mm to 2 mm away from the object.
3. Draw thin, straight lines: Use a hard pencil or fine pen with a set square or T-square.
4. Keep lines at right angles: Draw projection lines perpendicular to the dimension line.
5. Draw the dimension line: Place it between the projection lines, clear of the object.
6. Extend beyond the dimension line: Let projection lines pass 2 mm to 3 mm beyond the dimension line.
7. Add arrowheads or ticks and the figure: Complete the dimension neatly.

1.1.1.5 Hidden detail line

• Dashed Lines: Represent hidden features or elements not visible in the current view, such as beams inside walls or foundations below floor level.

A hidden detail line is a medium or thin dashed line used to show edges and features that exist but cannot be seen from the viewpoint of the drawing, because they are behind or inside other parts. It allows important information, such as foundations below ground, beams above a ceiling or pipes inside a wall, to be shown without drawing a separate view. Dashes are usually about 3 mm to 4 mm long with gaps of about 1 mm, kept uniform across the drawing. Example: on the plan of a farm store, the drafter used hidden detail lines to show the outline of the foundation footing beneath the walls and an overhead beam across the doorway.

Uses of Hidden Detail Lines

• Foundations: Showing footings and foundation walls below ground level.
• Overhead elements: Showing beams, roof edges and overhangs above the cut plane in plans.
• Concealed services: Showing pipes, ducts and cables inside walls or under floors.
• Hidden edges in views: Showing edges behind visible surfaces in elevations.
• Future or existing work: Indicating elements to be removed or added later, where conventions allow.

Guidelines for Drawing Hidden Detail Lines

• Keep dashes uniform: Use equal dash lengths and gaps throughout the drawing.
• Start and end with a dash: Hidden lines should touch the outline they meet, not leave a gap.
• Meet at corners with dashes: Where hidden lines meet at a corner, the dashes should join.
• Leave a gap when continuing a visible line: Where a hidden line continues straight on from an outline, start with a gap.
• Use only where needed: Too many hidden lines make a drawing confusing.

Other Line Types

• Phantom Lines: Depict alternate positions of movable parts or adjacent objects, such as door swings or furniture placement.
• Section Lines (Hatching): These lines fill cut surfaces in sectional views, showing materials or distinguishing between different elements.

1.1.2 Equipment specifications for line drafting

• Mechanical pencils ensure consistent line width and reduce smudging.
• Technical pens provide permanent ink lines for final drawings.
• The T-square is essential for maintaining horizontal line accuracy.
• Set squares assist in drafting vertical and angled lines precisely.
• Drafting compasses are necessary for accurate arcs and circles.

1.1.3 Line drafting procedures

1. Prepare the drawing surface by cleaning the drafting board and securing the drawing sheet to prevent movement.
2. Select the appropriate drawing tool based on the line type and thickness required.
3. Use the T-square to draw horizontal guidelines, ensuring they are parallel and evenly spaced.
4. Employ set squares to draw vertical and angled lines, aligning them carefully with the T-square edges.
5. Draw continuous thick lines for visible outlines, applying steady pressure for uniform thickness.
6. Use lighter pressure or thinner tools for dimension and detail lines, ensuring they do not overpower main outlines.
7. Incorporate dashed or chain lines where necessary, maintaining consistent dash lengths and spacing according to BS 8888.
8. Label lines appropriately using standard architectural notation and lettering styles.
9. Review the drawing for line clarity and correctness, erasing any stray marks or uneven lines.
10. Fix the final drawing using appropriate fixatives if working with pencils to prevent smudging.

1.1.4 Standards and conventions for lines in architectural drawings

• Line Thickness: BS 8888 specifies three main thicknesses: thick lines (0.7-1.0 mm) for visible outlines, medium lines (0.5 mm) for hidden or section lines, and thin lines (0.18-0.25 mm) for dimensioning and hatching.
• Line Types: Continuous, dashed, chain, and phantom lines must follow standard patterns, with dash lengths and spacings defined in ISO 128.
• Line Hierarchy: Visible outlines take precedence over hidden and centerlines to avoid confusion.
• Scale Considerations: Line thickness must be adjusted according to drawing scale; larger scales require thicker lines for visibility.
• Title Block and Line Identification: Each drawing sheet should include a title block with drawing details and a legend explaining line types used.

Chapter Summary

This chapter focused on producing plane geometry drawings by first exploring various types of lines used in drafting, including outline, break, centre, projection, and hidden detail lines, each serving a distinct purpose in technical drawings. The process of dividing lines and circles into equal parts was then examined, providing foundational skills for accurate geometric constructions. A comprehensive study of plane geometric forms followed, covering the construction of circles, triangles, rectangles, parallelograms, polygons, pyramids, conic sections, prisms, and loci, all essential for precise and clear technical representation. The chapter also detailed methods for constructing angles and the techniques for bisecting them accurately. Finally, the construction of scales was presented, enabling the creation of drawings to scale for practical application. Together, these topics equip learners with the essential procedures and standards for producing accurate, standardized plane geometry drawings.