xceptone, the original maps are in the sizes ie small medium & large maps, but the galaxy forge maps show up in the galaxy forge group.
the sequence of map groups is
small
medium
large
map designer (in the map designer folder next to the mods folders)
galaxy forge ( in the galaxyforge folder next to the mods folders).
sins 1.15+ & entrenchment 1.00+ all use mapversion 3.
if you have sins 1.15/entrenchment 1.00/1.01 then the maps also have to be added to the galaxy.manifest in the entrenchment folder, but I would suggest updating your sins with impulse to the current 1.03 as there are several bugfixes and balance fixes in the 1.03
also if you are using an old galaxyforge to create the maps then you need to use the map updater to update the maps to version 3 as there is a LOT more than just a version number change
harpo