Wrong Keymap used in X session

[Mathieu Malaterre <mathieu.malaterre@gmail.com>]

Hi there,

  I just finished installing a brand new debian/stable system on a
DELL Precision M6300... but I already have a problem with the keymap
used on my X session (console Ctrl-Alt-F1 is ok). In the
device-console keymap is British, but when I switch to the X session
(gnome) it is set to american.

  Every single package is from stable or stable/backports. Where do I
specify which keymap to use ?

Thanks
-- 
Mathieu