Proximity — Operator family

Proximity Operators work with distance: they grow or shrink shapes, describe how far every place is from something, or find the shortest connection between things. Most location questions (“close to”, “within walking distance”, “not too near”) end up here.

Part of the Operators families. Used in: Distance to habitat (Task), Habitat network (Task), Network gaps and stepping stones (Task), Nature content layer (Task).

Dilation (the ordinary buffer)

Operator Schema: every shape grows outward by a distance d. A point becomes a circle, a line a strip, a polygon a larger polygon that includes the original.

Choices to record: the distance and why; whether overlapping results are merged (that is a second Operator, dissolve); the shape of line ends (round or flat).

Note: a dilated lake includes the lake. “Close to the lake” usually means the fringe, not the dilation.

Tools: QGIS Buffer (Tool - QGIS) with a positive distance.

Erosion (negative buffer)

Operator Schema: every polygon shrinks inward by d. Parts narrower than 2 × d disappear.

Choices to record: the distance; what it means that thin parts vanish (a narrow woodland strip has no “core”).

Tools: QGIS Buffer (Tool - QGIS) with a negative distance.

Fringe (outer edge)

Operator Schema: the zone outside a shape up to distance d, without the shape itself: dilation, then the difference with the original. “Near the lake, but not in it.”

Tools: no single QGIS Tool. Buffer (Tool - QGIS) followed by Difference (Tool - QGIS).

Margin (inner edge)

Operator Schema: the zone inside a shape within distance d of its edge: the original minus its erosion. The forest edge, as opposed to the forest core.

Tools: Buffer (Tool - QGIS) with a negative distance, then Difference (Tool - QGIS) (original minus eroded).

Distance surface

Operator Schema: a raster where every cell holds the distance to the nearest target cell. Unlike a buffer it answers “how far” for every place at once, not just “within d or not”.

Choices to record: cell size (it sets the precision: 10 m cells give distances in 10 m steps); straight-line distance or distance along a network or across a cost surface (this family covers straight-line distance only).

Tools: QGIS Rasterize (Tool - QGIS) to make the targets a raster, then Proximity (Tool - QGIS).

Shortest line

Operator Schema: for each feature in one layer, the shortest straight line to the nearest feature in another layer. It shows where a gap is narrowest.

Choices to record: to the nearest point on the target or to its centroid (nearest point is almost always what is meant); how many neighbours; a maximum distance.

Tools: QGIS Shortest line between features (Tool - QGIS).

Kernel density

Operator Schema: each point is spread over a circle of radius r, weighted towards the centre, and the circles are added into a raster surface: a density without zones.

Choices to record: the radius (it plays the role zones play in an aggregation: a small radius shows streets, a large one districts); the cell size; the kernel shape; raw or scaled values.

Tools: QGIS Heatmap (Tool - QGIS).