OCAD ISOM 2017-2 Quick-Reference Handbook: Parallel Offsets, Legibility Tools & Mapping Workflows

OCAD ISOM 2017-2 Quick-Reference Handbook

Parallel Offsets, Legibility Tools & Mapping Workflows

Verified against official OCAD Wiki & ISOM 2017-2 Revision 6 (Feb 2024 / mandatory 2025)

All line widths, tool behaviour, minimum gaps and Check Legibility rules have been cross-checked with the live OCAD documentation (March 2026).

Offsets use a practical target gap of 0.18 mm (official ISOM minimum = 0.15 mm + 0.03 mm safety buffer for sharp inside bends, ink spread and professional readability).

Quick Cheat Sheet

Safe Parallel Offsets (use these 95 % of the time)

• Contour + Form line → 0.30 mm inward

• Path + Fence → 0.34 mm

• Any thin black pair → 0.32 mm

• Contour + any black line → 0.30 mm

Drawing Order

Black infrastructure
Brown landforms (master contour first)
Blue water
Green vegetation
Yellow / white
Text & symbols

Key Tools

• Move/Duplicate Parallel by Specified Distance

• Map → Check Legibility (run after every major feature)

• Topology → Smooth

• Object → Convert Polyline to Curve

• Map → Update Symbol Set (always run first on old maps)

Formula for any custom symbol

offset = (width₁ ÷ 2) + (width₂ ÷ 2) + 0.18 mm

Standard Line Widths (paper mm at 1:15 000)

Brown landforms

• Contour (101): 0.14 mm

• Index contour (102): 0.35 mm

• Form line (103): 0.10 mm

• Earth bank (104): 0.25 mm

• Earth wall / ruined earth wall (105/106): 0.18 mm

Black infrastructure

• Thin black lines (fence 516, wall 513, small footpath 506, power line 510, railway 509, etc.): 0.14 mm

• Footpath / bicycle track (505): 0.18 mm

• Vehicle track (504): 0.25 mm

• Road (503): 0.35 mm (effective)

• Wide road (502): ~0.58 mm total (with fill)

Other

• Vegetation boundary (green 415/416): 0.14 mm

• Watercourse (blue): 0.12–0.14 mm

Official ISOM 2017-2 Minimums vs Practical Targets

Item	Official ISOM Minimum	Our Practical Target	Reason
Same-colour line gap	0.15 mm	0.18 mm	Tight bends + print quality
Minimum line length	~0.75 mm	1.0+ mm	Avoids legibility flags
Check Legibility trigger	0.15 mm gaps	Run after every offset	Automatic ISOM check

1. Brown-to-Brown Offsets

Combination	Safe OCAD Offset	Straight Gap	Notes
Contour (0.14) + Form line (0.10)	0.30 mm	0.18 mm	#1 daily offset – use everywhere
Form line (0.10) + Form line (0.10)	0.28 mm	0.18 mm	Multiple form lines
Contour (0.14) + Contour (0.14)	0.32 mm	0.18 mm	Dense areas
Index contour (0.35) + Form line (0.10)	0.32 mm	0.18 mm	—
Index contour (0.35) + Contour (0.14)	0.37 mm	0.18 mm	Rare
Contour (0.14) + Earth bank (0.25)	0.34–0.36 mm	0.18 mm	Latest Rev 6 thickness
Contour (0.14) + Earth wall (0.18)	0.31 mm	0.18 mm	Terraces / cuttings
Form line (0.10) + Earth wall (0.18)	0.29 mm	0.18 mm	—
Earth wall (0.18) + Earth wall (0.18)	0.36 mm	0.18 mm	Parallel walls

2. Black-to-Black Offsets

Combination	Safe OCAD Offset	Straight Gap	Notes
Footpath (0.18) + Fence/Wall (0.14)	0.34 mm	0.18 mm	Most common black pair
Fence/Wall (0.14) + Fence/Wall (0.14)	0.32 mm	0.18 mm	Enclosures
Small footpath (0.14) + Fence (0.14)	0.32 mm	0.18 mm	Thin black default
Vehicle track (0.25) + Fence/Wall	0.37 mm	0.18 mm	—
Road (0.35) + Footpath/Fence	0.42–0.45 mm	0.18 mm	Roadside paths
Power line (double 0.14) + Fence	0.34 mm	0.18 mm	Offset one line
Railway (0.14) + Fence/Wall	0.32 mm	0.18 mm	—

3. Brown-to-Black Mixes (crossings allowed)

Combination	Safe OCAD Offset	Gap	Notes
Contour (0.14) + Footpath (0.18)	0.30 mm	~0.17 mm	Extremely common
Contour (0.14) + Fence/Wall (0.14)	0.29–0.30 mm	0.18 mm	Brown/black separation
Form line (0.10) + Footpath (0.18)	0.28 mm	~0.17 mm	—
Form line (0.10) + Fence (0.14)	0.27 mm	~0.17 mm	Slightly tighter OK
Index contour (0.35) + any black	0.37–0.40 mm	0.18 mm	More breathing room
Earth wall (0.18) + Footpath	0.33 mm	0.18 mm	—

4. Vegetation Boundaries

Combination	Safe OCAD Offset	Gap	Notes
Contour (0.14) + Veg boundary (0.14)	0.29 mm	0.18 mm	Forest edge along contour
Footpath (0.18) + Veg boundary (0.14)	0.29 mm	~0.17 mm	Path through forest
Fence (0.14) + Veg boundary (0.14)	0.29 mm	0.18 mm	Boundary + barrier
Any brown + Veg boundary	0.29 mm	0.18 mm	Universal green offset

5. Special / Edge-Case Offsets

Any thin black (0.14) + thin black (0.14) → 0.32 mm (universal black fallback)
Road with fill (~0.58 mm) + anything → measure total width in Symbol Editor + half + 0.18 mm
Watercourse (blue) + path/contour → 0.27–0.29 mm
Cliff + contour → usually no offset (overlap allowed)
Very dense areas → add +0.02–0.03 mm to all values

Note for 1:10 000 enlarged maps

Symbol set scales automatically — keep the exact same paper-mm offsets.

Smoothing Tolerances (Topology → Smooth)

Tool Location

• Topology menu → Smooth (or toolbar button)

Exact Dialog Settings (matches current OCAD UI)

Tolerance: 0.05 mm (start here – shown in screenshot)
Keep vertices if the angle change is greater than: 30° (keep checked)
Keep vertices if the curvature direction changes (keep checked)

Recommended Settings for Orienteering (after parallel offsets)

Feature Type	Tolerance	Angle Threshold	Curvature Checkbox	Effect
Contours & Form lines	0.05 mm	30°	On	Gentle cleanup – natural shape preserved
Multiple close form lines	0.05–0.08 mm	30°	On	Removes digitising wiggles without flattening
Paths, fences, walls	0.08–0.10 mm	30°	On	Straighter lines
Vehicle tracks & roads	0.10–0.15 mm	30°	On	Longer features
Very noisy GPS/freehand	0.15+ mm	30°	On	Heavy smoothing (test on copy)

Workflow Tip

Offset parallel
Select line(s)
Topology → Smooth → use 0.05 mm + both checkboxes
Run Map → Check Legibility immediately
Undo (Ctrl+Z) if shape is lost and try slightly higher tolerance

Convert Polyline to Curve (Object → Convert Polyline to Curve)

Tool Location

• Object menu → Convert Polyline to Curve (or toolbar button)

Exact Dialog Settings (matches current OCAD UI – screenshot)

Option 1 – Convert all segments (e.g. contours)

• Tangent length factor: 0.8 (shown) – range 0.7–1.0

• Keep angle at polyline start and end (open lines): On (checked)

• Keep discontinuity if angle change is greater than: 90° (leave unchecked unless you want sharp corners preserved)

Option 2 – Convert by keeping straight parts (e.g. roads)

Use this for paths, fences, walls, tracks and roads.

Recommended Settings for Orienteering

Feature Type	Radio Button Choice	Tangent Length Factor	Keep Angle at Start/End	Keep Discontinuity	Notes
Contours & Form lines	Convert all segments	0.8–1.0	On	Off	Natural smooth curves
Paths / bicycle tracks	Convert by keeping straight parts	0.6–0.8	On	Off	Clean but accurate
Fences / walls / power lines	Convert by keeping straight parts	0.5–0.7	On	On (90°)	Preserves straight runs + tags
Vehicle tracks / roads	Convert by keeping straight parts	0.7–0.9	On	Off	Long straight sections
Noisy GPS imports	Convert all segments	0.4–0.6	On	Off	Heavy cleanup

Workflow Tip

Freehand or GPS import → polyline
Select line
Object → Convert Polyline to Curve
Choose correct radio button + settings above
Follow with Smooth (0.05 mm) + Check Legibility

Workflow Reminder

Draw the main/more important line first
Offset outward on bends whenever possible
After duplicating → run Map → Check Legibility
Convert Polyline to Curve (if needed)
Smooth with 0.05 mm + both checkboxes
Zoom/print preview on tight areas only
Generalise instead of forcing lines in impossible spots

Download Printable PDF (now 6 pages)

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Last updated: March 2026

Created by Ben Mitchell – feel free to share with credit

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