Can you clarify when data compression is used?

[Kevin Hilton]

Im aware of the personal cipher preferences and personal hash
preferences, but when talking about the defaults I specifically asking
if gpg were installed from source -- no modifications made -- and gpg
keys were created - what default cipher and hash would be listed first
in the list with the keys?

Without any intervention
gpg-key-gen

It appears to manually choose a DSA signing key (DSA vs DSA2 --
ambiguous since the man pages contain a switch to --enable-dsa2 in the
gpg.conf file) with SHA1 hash -- or at least the SHA1 hash is ranked
first in the key preference list

For the encryption key - a ElGamal 2048 bit key is the default with
AES chosen as the first cipher contained in the key cipher preference.

Basically I'm aware of the --default-preference-list option in the
gpg.conf file that control preferences during key generation.  I know
how to use this option, but sadly I think the explanation is really
lacking:
--default-preference-list string
          Set  the list of default preferences to string.  This prefer-
          ence list is used for new keys and becomes  the  default  for
          "setpref" in the edit menu.

What I want to know is obviously GnuPG comes with a
--default-preference-list "built-in".  If I dont specify this setting
in the gpg.conf file, what string is used by default?  This would
basically reveal the order and list of all the defaults for ciphers,
hashes, and compression settings.