The mapping.<distribution> format is as follows:
<distribution package name>/<SMGL package name>

e.g. for Gentoo:
vim-core/vim

This will map Gentoo's vim-core to SMGL's vim.

This is done by convert2smgl.sh calling the following:
for i in <mapping file>
do
  <package list>=${<package list>/$i}
done

e.g. for Gentoo

for i in mapping.gentoo
do
  GENTOO_PACKAGES=${GENTOO_PACKAGES/$i}
done

If we don't have the package, then do the following:
<distribution package name>/

e.g. for Gentoo's sysvinit package
sysvinit/


This will remove sysvinit from the list