Adding Features - Buffer (Add Menu)

📖 Overview

The Buffer function allows you to create new geometry for an overlay based on an existing object.

• The object can be on the overlay, the basemap, or drawn during the process.

• Buffers are useful for spatial analysis or creating overlay data features.

A buffer is generated by drawing a line in parallel to, or at a fixed distance from, the original polyline or polygon.

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🧭 Understanding Buffers

• Polyline Buffer → Looks like a “sausage” with circles at both ends.

• Polygon Buffer → Resembles the polygon shape.

  • Positive offset → Buffer is larger than the original polygon.

  • Negative offset → Buffer is inside the original polygon.

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➕ Adding a Buffer to an Overlay

1️⃣ Start the Buffer Tool

• Click Add > Buffer.

• Menu options will grey out, and Abort / Confirm toolbar buttons activate.

• Right-click to open the popup menu for buffer creation tools.

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2️⃣ Option A — Create a New Feature Using a Buffer

• While in Add Buffer mode, draw the object to buffer (e.g., a polyline down a road’s centre).

• Press F4 or right-click > Finish.

• Enter the buffer offset in the Specify Offset dialog (e.g., 20m each side).

• The buffer is created as a new overlay feature, ready for attribute entry.

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3️⃣ Option B — Buffer an Existing Overlay Feature

• Useful for safe zones or catchment areas.

• Snap to the existing polygon/polyline/point via right-click > Snap.

• Tick Include all of polygon if needed.

• Finish drawing, enter the offset, and a precise buffer will be created around the geometry.

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🔄 Negative Buffers

• Specify a negative offset (e.g., -10) to create a buffer inside the polygon.

• May result in multiple internal buffer geometries if the original shape is irregular.

• Holes inside polygons are respected for internal buffers.

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🖼 Examples

📍 Example 1 — 50m Outside a Site Boundary

1. Add Menu > Buffer. 

2. Click polygon > Right-click > Snap.

3. Tick Include all of polygon.

4. Finish drawing (F4).

5. Enter offset 50m.

6. Confirm → Complete data form → Save.

Click the Confirm button to take you to the overlay data form to complete the text record for the new feature, then Save in the normal way.

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📍 Example 2 — Inside Polygon at Least 15m from Boundary

1. Same steps as Example 1.

2. Enter offset -15. 

3. Buffer shows the internal safe zone.

   

⚠️ If the offset is too large, no buffer will be created.
⚠️ Multiple geometries may result from irregular shapes.

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📝 Additional Notes

• Buffers can be created from points, lines, or polygons.

• Snapping is recommended for precision.

• Add Buffer uses the line geometry of the polygon’s outline.

• Holes in polygons cannot be auto-buffered directly but are honoured when creating from overlay polygons.

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⚡ Performance Considerations

• Buffering is processor-intensive.

• Large polygons or offsets (>1000m) take longer to process.

• Example: Largest polygon + 2500m offset = ~45 seconds.

• Suggested: Use one CPU core to keep working while buffering.

• Large buffers can sometimes be approximated more simply (e.g., buffer a central point with a circle).