Transferring from https://bugzilla.gnome.org/show_bug.cgi?id=694623#c4 .

I noticed something about the keyboard layout preview widget today; it respects
the xkb 'geometry' setting in determining what physical keys to draw. In
practice, with the evdev ruleset - which I think everything uses these days -
that setting will almost always be 'pc104', which is the geometry used by a
US-style keyboard with Windows keys (pc101 is US-style without Windows keys).
When drawing a preview of a layout which is more commonly associated with the
'pc105' or 'pc102' physical keyboard - where the enter key and one other key in
that neighbourhood are different, and there is an extra key between the left
'shift' key and the first alphanumeric key on the row above space (Z on a US/UK
layout, Y on German, probably something else on other layouts) - this looks
rather odd and means one key is missing.

If it just defaulted to 'pc105', though, I suppose the illustration of the
normal US layout (and any other layouts which use the 101/104-key physical
keyboard) would be wrong.

To get it exactly right there'd need to be a source of data about which
keyboard layouts are most commonly associated with which geometries, I guess,
and the place to put that would probably be langtable. But there's a fairly
simple approximation you can use that looks like it'd be correct most of the
time: if the layout is a US variant then use the pc104 geometry, if it's
anything else, use the pc105 geometry. From a quick peruse of
https://en.wikipedia.org/wiki/QWERTY , https://en.wikipedia.org/wiki/QWERTZ ,
and https://en.wikipedia.org/wiki/AZERTY it looks like most everything that
isn't a US variant uses the pc105 geometry, the exceptions being a few which
use an oddball geometry which looks like pc104 around the Enter key but has the
extra key between left shift and Z, and Vietnamese and "Turkish Q", which use
the pc104 geometry.