Operators — the families
An Operator is one tool-agnostic transformation of spatial data: buffer, clip, dissolve, zonal statistics. Operators are kept simple: each does one thing. A Tool is what a software Stack bundles into one dialog, and one Tool can realise several Operators through its options (see Terminology Glossary, §9).
Operators are grouped in families: Operators that do the same kind of work. The families are the index to search when a new problem comes up. They are domain-neutral: the same Proximity Operators measure walking distance to a park in urban design and link habitats into a network in landscape ecology. What differs is the domain that uses them.
| Family | What it does | Operators |
|---|---|---|
| Selection | Keeps some features or cells, drops the rest | by attribute, by location |
| Overlay | Combines two layers as sets | intersection, union, difference, symmetric difference, clip |
| Proximity | Works with distance | dilation, erosion, fringe, margin, distance surface, shortest line |
| Geometry restructuring | Changes how geometry is split into features | merge, dissolve, explode |
| Geometry generation | Creates new geometry by a rule, as a frame for other data | generate grid |
| Aggregation | Summarises many values into one per zone or group | summary by location, zonal statistics, tabulate area, group-by statistics |
| Attribute calculation | Derives new values per feature or per raster cell | recode, indicator (0/1), ratio, aggregate over a group, map algebra |
| Conversion and data management | Changes the form or extent of data, without changing what it says | rasterize, polygonize, reclassify, clip to extent, reproject, save |
From problem to Operators to Tools
- Write the problem as a Task (for example Habitat network (Task)): the decisions it needs and the Operators that carry it out (see C - Authoring the Recipe).
- Find each Operator in its family and read its choices: they are the decisions the Task must record.
- Only then look up the Tool that realises the Operator in your Stack, for QGIS in the Tool notes (Buffer (Tool - QGIS) and the others linked from each family).
Asking an AI assistant
A question about a whole problem (“how do I find connected habitats in QGIS?”) gets a general answer that is hard to check. A question about one step of a Task gets a precise one:
I am doing step 3 of my Task: dilate all nature patches by 50 m and dissolve them into clusters, keeping separate clusters as separate features. Which QGIS 4.2 tool does this, with which parameters, and what can go wrong?
The assistant then works on the Extent (which tool, which settings), and you keep the Intent (what the step is for and why 50 m). Check its answer against the Tool notes here, and against the tool’s own help text in QGIS.