Converting rasters to vectors

Sometimes, you need to convert data that is originally in raster format to a vector format in order to perform vector-based analysis methods. Generally speaking, as rasters are continuous datasets, converting them to polygons is more common than converting them to lines or points.

Getting ready

You need a raster layer, preferably one with groups of the same valued pixels next to each other. For this example, we'll use geology_30m.tif, as a 30 meter x 30 meter pixel should give decent results.

Tip

The smaller the pixels, the smoother looking the resulting vector will appear when zoomed out.

How to do it…

1. Load geology_30m.tif.

2. Go to Raster | Conversion | Polygonize:

   

3. Name the output geology_30m.shp.

4. (Optional) Name the output column geology, class or value.

5. Press OK to run the process.

6. Compare the results (colors are in a similar but different scale):

   

How it works…

For each pixel, the value is compared to its neighbors (there are different neighbor algorithms). When two pixels...