This came up in a game today.

Iet A and B = areas next to the Imperial Palace. Let C and D = outer areas of the Imperial Palace. If I as the traitor player declare an Assault against area D, can units and heroes in area A participate in the Assault? The definition of two adjascent regions is two areas that share a border, but my opponent argued that a single point does not constitute a border....

A | C

---------------

B | D

The rules don't mention it directly, but the paragraph "Breaches" on page 33 mentions that fortified areas have border segments which are a "length of border". As the point has no length, it has no border segment and thus is no border. Accordingly the areas are not adjacent which of course also counts for unfortified areas. This means attacks and movement over the point are impossible.

But even if the rules didn't say anything, common sense should tell you that the point doesn't make the areas adjacent, unless the rules explicitly say that. This is true for almost all games with uneven areas (unlike areas which are perfect squares for example).