Converting Rasters to Polygon Features
This tutorial demonstrates using the Polygonize (raster to vector) tool in QGIS, which converts raster datasets to polygon feature classes based on raster cell values (and replicates those values within the output feature class’s attribute table).
Included in this tutorial:
Accessing the Polygonize (raster to vector) Tool
Tool Parameters and Example
Software version in examples: QGIS-LTR 3.44.10-Solothurn
Tutorial Data: The tutorial includes demonstration with sample data available here.
Credits: Sally Kaye and L. Meisterlin (2026)
Accessing the Polygonize (raster to vector) Tool
You can access the Polygonize (raster to vector) tool through the Processing Toolbox by clicking through GDAL > Raster conversion > Polygonize (raster to vector).
Alternatively, you can find it in the menu bar through Raster > Conversion > Polygonize (raster to vector).
accessing the Polygonize tool
Tool Parameters and Example
In the Polygonize (Raster to Vector) dialogue box, use the dropdown menu to select your Input layer and Band number for multiband rasters.
Type in the text box to name the attribute field that will be created based on the raster cell values. For multiband rasters, converting to vector will create multiple attribute fields.
Optional: Click the checkbox to use 8-connectedness which considers diagonally connected raster cells (pixels) when defining a contiguous area in addition to the standard 4 cells (top, bottom, left, and right).
By default, the new vector layer will open as a temporary layer in the project. Click the three dots to name and save your layer to files.
In the example below, we start with an input raster (“RasterShapeLength”) created by converting the Tracts_Points1_join layer to a raster using the “shape_length” field. We name the new field “ShapeLength.”
converting a raster layer to polygon features
Examining Output Geometry
The result of the Polygonize (Raster to Vector) tool is a feature class of polygons that preserve the outlines of the source raster layer cells. This is visible below.
polygon edges are “pixelated” according to the input raster cell size
Examining the Output Attribute Table
The output polygon attribute table includes a feature ID as well as a field corresponding with the raster cell values (in our example case: “ShapeLength”).
the attribute table of the output polygon layer