I have a raster map which I have extracted from a government report providing flood extent return frequencies. I want to 'snatch' these flood extent polygons (i.e. convert to vector) and I was wondering if there is a simple way to do this in QGIS. Simply digitising these layers by tracing new polygons would be too time consuming and potentially result in human error.
Is there a tool or methodology someone could recommend to me which would recognise these polygons in raster format (there are clearly outlined and coloured distinctly differently to the background) so I can convert them to vector?
Any help with this is very much appreciated.