I am working with QGIS. I used raster-extract-contour to get contour lines from a raster image. Now I want to break up my single vector file into multiple layers based on elevation. How do I do this?
You can do that while generating the contour lines. When you define the interval between contour lines in the Contour menu, you can provide an attribute name, in which the elevation will be attached as an attribute.
See also the tutorial, step 14.
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If you want to obtain one layer for every attribute in a specific field then you could to use "Split vector layer" in:
Processing Toolbox >> QGIS Geoalgorithms >> Vector general tools