Conversion and data management — Operator family
These Operators change the form, extent or storage of data without changing what it says: from vector to raster and back, from codes to classes, from the whole country to the study area. They are rarely the point of an analysis, but every analysis needs them, and each one involves a choice that can change the result.
Part of the Operators families. Used in: Distance to habitat (Task), Network gaps and stepping stones (Task), Aggregating a categorical raster to zones (Task).
Rasterize
Operator Schema: vector features become raster cells, with a fixed value or a value from a field.
Choices to record: cell size; which cells count as covered (by default a cell is burned when its centre is inside the polygon, so features narrower than a cell can disappear); extent.
Tools: QGIS Rasterize (Tool - QGIS).
Polygonize
Operator Schema: connected cells with the same value become polygons.
Tools: QGIS Polygonize (raster to vector) (Raster conversion).
Reclassify
Operator Schema: cell values are replaced according to a table of ranges or values: land-use codes to “farmland yes/no”, distances to distance classes.
Choices to record: the class boundaries, and whether a boundary value belongs to the class below or above.
Tools: QGIS Reclassify by table (Raster analysis).
Clip to extent
Operator Schema: keep only the part of a layer inside a rectangle, typically the study area plus a margin.
Choices to record: the margin. An analysis that stops exactly at the study area boundary treats everything outside as missing: a patch just outside the area is still part of the network.
Tools: QGIS Clip raster by extent (Raster extraction); for vector layers Clip (Tool - QGIS) with a rectangle, or Package layers (Tool - QGIS).
Reproject
Operator Schema: coordinates are transformed to another coordinate reference system. Danish data belong in ETRS89 / UTM zone 32N (EPSG:25832), where distances and areas are in metres.
Tools: QGIS Reproject layer; Package layers (Tool - QGIS) can reproject while saving.
Save
Operator Schema: write a layer to a file, usually a GeoPackage.
Tools: QGIS Export › Save Features As…, or Package layers (Tool - QGIS), which saves several layers into one GeoPackage with a common clip extent and their styles.