I just downloaded the latest Polaris (2017-04-28) and flashed it to a new SD card. When installing on my Pi-Top (not CEED), I can select a keyboard - only none of the four images (UK, US, German or Spanish) match my keyboard layout.
On my keyboard the bottom row is:
fn | ctrl | <> | alt | Space | alt | pi-top | ctrl | < | v | >
where <> is actually stacked, and <, v and > are the left, down and right arrows.
I chose US, since it doesn't show the alt-gr key, and the <> key works correctly. But it was definitely confusing!