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When I download DEMs for a diagonal section of coastline, I am forced to download a rectangular area, which leaves gigabytes of unused data. I want to delete the DEM files for the areas I don't need.

After building my map in QGIS, by importing ASC files as raster layers, is there a way to draw a selection, and remove all layers within that selection or another quick way to delete unwanted DEMs/ASC files?

This describes how to select features within a layer for deletion. My goal is to select layers on the map for deletion.

John Newman
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  • The end-goal is to delete the files from the hard drive. Whatever achieves that goal in the fewest steps is the ideal solution. – John Newman Jan 27 '22 at 08:22
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    Easier is to select all you need and delete everything else. – Gery Feb 13 '22 at 20:37
  • mmmmm not sure how to do it in QGIS, I would do it programatically in linux using a combination of linux-based tools and GIS tools (e.g., gdal). I would first find a way to filter the ones I need (perhaps you can select them within a region of interest? or filter them by their names?) and then move them to an another directory. This would be my first practical attempt to solve this. – Gery Feb 15 '22 at 15:09
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    Thanks @Gery - someone helped me find a solution today which matches your idea: merge raster files into one layer first, create a polygon shapefile representing the areas you want to keep, then "clip raster by mask layer" using that shapefile. Posted the solution below. – John Newman Apr 10 '22 at 07:11

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  1. Merge all the raster layers. Raster>Miscellaneous>Merge
  2. Draw a polygon shapefile representing the area you wish to keep. Layer>Create Layer>Shapefile (polygon)
  3. Crop the merged raster file using the shapefile as a mask, save permanently. Raster>Extraction>Clip raster by mask layer
  4. Delete original raster files!

Thanks to QGIS Community - Official Virtual Group for helping me find the solution.

John Newman
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