Geometry processingGeometry processing

Reshape existing features with Buffer, Simplify, Smooth, Break apart, and Merge.

Buffer, Simplify and Smooth modify the geometry of an already-drawn feature. They appear in the editing toolbar (and the feature's right-click menu) when a single Polygon, MultiPolygon, LineString or MultiLineString is selected; they are not offered for points or geometry collections. All three show a live ghost preview before you commit, so you can tune the result without permanently altering the feature. The previews are computed in a background worker, so the map stays responsive while you drag a slider.

BufferBuffer

Expand or contract a polygon by a fixed distance, or turn a line into the corridor polygon around it. Useful for proximity analysis (e.g. "everything within 200 m of this boundary" or "200 m either side of this road") or for rough offset shapes.

Supported geometry: Polygon, MultiPolygon, LineString, MultiLineString. The result is always a Polygon or MultiPolygon.

How to use

1. Select a single polygon or line feature.
2. Click Buffer in the editing toolbar.
3. Drag the distance slider. Positive values expand the polygon outward; negative values shrink it inward. Range: −500 m to +2,000 m (the slider is stored in metres regardless of the displayed unit). For a line the slider starts at 0: a line has no inside to shrink into, so a distance of 0 or less gives no preview and Apply stays disabled.
4. Toggle the unit label to switch between small / large display units. The pair follows config.units.length: m ↔ km for metric, ft ↔ mi for imperial. Storage is always metres — the conversion happens at the input boundary.
5. Choose whether to replace the original feature or create a new shape alongside it (the New shape toggle, on by default).
   • New shape on: the buffer is added as a new feature named "<source name> (buffer)", placed directly below the source in the layer list. The source feature is unchanged.
   • New shape off: the source feature's geometry is replaced by the buffer. For a line this means the feature becomes a polygon (same id, properties and schema).
6. Press Enter or click Apply to commit. Press Escape to cancel.

A dashed outline of the buffered shape updates as you drag the slider, leaving the original feature visible underneath. With New shape off, the original is drawn as a faint grey ghost instead.

Apply is a single undo step in both modes.

Notes

• The buffer preview is computed in a background worker, so the map stays responsive while you drag the slider. Only the latest slider value is kept; a computation that takes longer than 30 seconds is abandoned.
• Shrinking a polygon too far (below zero area) produces an empty result: the preview disappears and Apply stays disabled, so the feature is never replaced. The failure is reported to onError (no toast).
• A buffered circle, rectangle or route is a plain polygon afterwards: the result drops _drawType (and a route's properties._waypoints), so its vertices edit freely (no warning is shown). With Create new, the new polygon doesn't inherit _waypoints either.

SimplifySimplify

Reduce the vertex count of a polygon or line using the Ramer–Douglas–Peucker algorithm (@turf/simplify). Use this to clean up overly-dense geometry imported from external sources, or to reduce file size before export.

Supported geometry: Polygon, MultiPolygon, LineString, MultiLineString.

How to use

1. Select a single feature.
2. Click Simplify in the editing toolbar.
3. Drag the tolerance slider (0–100). The slider maps to a fraction of the feature's own bounding-box diagonal with a quadratic curve — small values at the low end give fine control, large values at the high end produce aggressive reduction. The label shows the resolved tolerance in your configured length unit (<1 m, 12 m, 1.4 km, etc.).
4. The node count change is shown in real time (e.g. "120 → 78 nodes (−42)").
5. Press Enter or click Apply to commit the simplified shape (one undo step). Press Escape or click Cancel to keep the original. Apply is disabled until the slider removes at least one node.

Notes

• Tolerance is adaptive: the same slider position produces a sensible result whether the feature is a 30 m GPS track or a country outline. The bbox diagonal sets the scale, so feature size doesn't matter.
• Simplification removes vertices. It never adds them.
• A line stays a line: its first and last points are always kept, so at the highest tolerance it collapses to a straight segment between its endpoints, never to nothing. Each part of a MultiLineString is simplified separately.
• Tolerance 0 is lossless; tolerance 100 caps at 30 % of the bbox diagonal — enough to flatten most natural shapes without collapsing them.
• Applying Simplify (or Smooth) to a circle, rectangle or route removes the _drawType constraint and a route's properties._waypoints: the shape becomes a plain polygon / line (no warning is shown).

SmoothSmooth

Add vertices to a polygon or line to produce a softer, rounder shape, using Chaikin corner cutting (Turf's polygon-smooth for polygons; the same scheme for lines, which stay open). Use this after importing sharp administrative boundaries, or to give manually-drawn areas a more natural appearance.

Supported geometry: Polygon, MultiPolygon, LineString, MultiLineString.

How to use

1. Select a single feature.
2. Click Smooth in the editing toolbar.
3. Drag the passes slider (1–5). Each pass adds vertices and rounds corners further. The node count change is shown (e.g. "40 → 168 nodes (+128)").
4. Press Enter or click Apply to commit (one undo step). Press Escape or click Cancel to cancel.

Notes

• Smooth increases vertex count. Combine with Simplify if the result is denser than needed.
• A smoothed line stays open: its first and last points don't move, only the corners in between are rounded. Each pass roughly doubles a line's point count. A line with only two points has no corners and is left as is.
• Like Simplify, Smooth strips _drawType from circles, rectangles and routes.
• At 5 passes, complex polygons may accumulate thousands of vertices. Check the vertex count delta before committing if file size matters.

Break apartBreak apart

Split a multi-geometry feature into individual features. Each part becomes its own entry in the feature collection, inheriting the original feature's properties, schema and group; the first part keeps the original's id. A circle, rectangle or route tag (_drawType) is dropped.

Supported geometry: MultiPoint, MultiLineString, MultiPolygon, and GeometryCollection (each member geometry becomes a feature; a Multi* member stays one feature, so break it apart again if needed). The feature needs at least two parts, and the extra features count against maxFeatures.

How to use

1. Select a single multi-part feature.
2. Click Break apart in the editing toolbar (or press B, the default shortcut).
3. The feature is immediately replaced by its parts, in one undo step.

MergeMerge

Combine two or more selected features of the same geometry type into a single multi-geometry feature.

Supported geometry: Any.

How to use

1. Select two or more features (Shift+click or lasso).
2. Click Merge in the editing toolbar.
3. The selected features are combined into a single multi-geometry feature. Properties from the first-selected feature are retained; properties from the others are discarded.

Notes

• Merge collects the parts without dissolving shared borders. Overlapping polygons stay overlapping parts. To dissolve them into one outline, use Union in Boolean operations.
• The merge result is a single undo step.