This video illustrates how the filter 'Arrays & tiles / Montage' of the G'MIC plug-in for GIMP can be used to quickly create complex layout from several input layers.
Get the G'MIC plug-in for GIMP at : http://gmic.eu/gimp.shtml
Credits :
Images by Patrick David (https://www.flickr.com/photos/patdavid/), distributed under CC-by-SA).
Musics : "MOUNTAIN SUN" by Jason Shaw (http://audionautix.com/index.html) and "Mavi Sepet" by Hayvanlar Alemi (www.hayvanlaralemi.org), distributed under CC-by-SA.