Geometry

The Geometry tools work on one layer at a time and write a reshaped copy of it. They answer questions of the kind “what is within 500 metres of this”, “what does this look like as one shape per district”, “what is the centre of each parcel”.

None of them modify your input layer. Each run adds a new layer to the map, named after the tool, so you can keep the original and compare.

Start here

Buffer

The tool you will reach for most often. It grows every feature by a fixed distance and returns the resulting polygons: a 500 metre band around a road, a 5 kilometre catchment around each clinic, a safety margin around a plot.

Parameter	What to set
Input layer	Any vector layer. Points give circles, lines give bands, polygons give a larger polygon.
Distance	How far to grow. Must be positive.
Units	Kilometres, metres or miles. Set this before the distance, so you do not buffer by 500 kilometres by mistake.

The buffers of neighbouring features may overlap. If you want a single continuous band instead, run Dissolve on the result.

Dissolve

Merges features into one geometry, which is how you turn a layer of parcels into the outline of a neighbourhood, or a set of overlapping buffers into one clean band.

Leave the Dissolve field empty to merge everything into a single shape. Name a field instead and you get one shape per distinct value of that field: one polygon per region, per land use class, per year.

If you also need a number per group, such as the total population or the mean value, use Aggregate by attribute rather than Dissolve.

Simplify

Reduces the number of vertices, using the Douglas-Peucker algorithm. Useful to lighten a coastline or an administrative boundary that carries far more detail than your map shows.

The Tolerance is expressed in degrees, so the numbers are small: 0.01 is roughly one kilometre near the equator, 0.001 roughly one hundred metres. Start low and increase until the shape starts to look wrong, then step back. High quality uses a slower but more faithful variant, worth enabling on shapes you care about.

Simplify makes shapes angular. To round corners instead, see Smooth.

Regular grid

Builds a fishnet of rectangular cells over an area, which is the usual first step before counting or summarising anything per cell.

Choose where the extent comes from: the map viewport as you currently see it, a layer extent, or a manual bounding box you type in. Then set the cell width and height, in degrees, and whether you want the cells as rectangles or as points at their centres.

For hexagons rather than rectangles, use the H3 toolbox.

All the tools

Tool	What it does
Buffer	Grows every feature by a fixed distance and returns the resulting polygons.
Centroids	Returns one point per feature, at its centre.
Convex hull	Returns the smallest convex polygon enclosing all the features, like a rubber band stretched around them.
Dissolve	Merges features into a single geometry, or into one geometry per value of a field.
Bounding box	Returns the rectangular envelope of all the features.
Simplify	Removes vertices with Douglas-Peucker, at a tolerance you choose.
Explode	Splits multipart features into one feature per part, keeping the parent’s attributes on each.
Aggregate by attribute	Merges features sharing a field value into one shape per group, with a count, sum, mean, min, max or median computed on a numeric field.
Smooth	Rounds the corners of lines and polygons with Chaikin’s algorithm, from 1 to 10 iterations. Adds vertices rather than removing them, and leaves points untouched.
Regular grid	Builds a rectangular fishnet over the viewport, a layer extent or a bounding box, as cells or as centre points.
Voronoi / Delaunay	From a point layer, builds either a Voronoi diagram, one polygon per point covering the area closest to it, or the Delaunay triangulation connecting the points.
Cell-site coverage	Builds antenna sector wedges from point sites, using an azimuth, a radius and a beamwidth taken either from attribute fields or from fixed values. Beamwidths above 360 degrees are treated as a full circle.

Notes

Distances. Layers are held in WGS 84, so the distance you type is converted from your chosen unit to degrees before the shape is built. That is accurate at the scale of a city or a region, and drifts at very high latitudes, where a degree of longitude is much shorter than a degree of latitude. For an exacting buffer far from the equator, check the result against the Measure widget.

Multipart features. A single feature can hold several disjoint shapes. Run Explode first if you need one row per shape, for instance to count islands or to label each part separately.