Buffer

A buffer produces a polygon around each input feature at a fixed distance. Points become circles. Lines become long thin polygons (think road right-of-way). Polygons grow outward (or shrink inward with a negative distance).

This page documents the Buffer step in isolation. It's a single derived-layer step and that's all it does on its own. Combine it with other steps via a derived layer's pipeline.

Inputs

• Source layer: any data layer or another derived layer.
• Distance: a number, positive (outward) or negative (inward on polygons).
• Units: meters, feet, kilometers, miles.

Output

A new layer whose geometry is ST_Buffer(source.geometry, distance) for each input row. Attributes are copied from the source row verbatim.

How to use it on its own

1. Open the new-item wizard and pick Derived layer.
2. Pick a Source. The layer you want to buffer.
3. Add a Buffer step.
4. Enter the distance and pick the unit.
5. Click Save.

That's the whole single-step recipe. Nothing else is required.

Example

You have a points layer of fire hydrants and want to know the area each one covers. Buffer the layer by 300 feet. The output is a polygon layer where each polygon is the 300-foot service area of one hydrant.

That's it. No dissolve. No centroid. No "first you join, then you...". Just buffer.

Notes

• Distance is geodesic. We project to a local equal-area CRS, buffer there, then reproject the result. This makes the 300-foot example actually 300 feet on the ground regardless of the layer's source CRS.
• Negative distances only do something useful on polygon inputs. A negative-buffered point becomes the empty geometry (and is dropped from the output).
• Buffered geometry doesn't update live if the source layer edits geometry. Buffered layers are materialized. Hit the Refresh button on the derived layer's detail page to recompute.