which default to write

hi, For the creation of deployment dmg's i started to use InstaDMG. The idea of manipulating things using pkgs is somewhat harder to implement but it's a lot more 'recyclable' in other deployment scenarios. By harder to implement i mean: how can we know which default to write for a particular setting? is there a public list available? for example, i want a different keyboard layout by default. how do you guys figure out which default to change to which value?