Can we make isoglosses?

[Koen G]

Of course, a pre-requisite to access studies in the field is a good knowledge of German: I certainly don't qualify 

This is also a big problem for me. Studies of German dialects are understandably written in German. I have never studied German, and the understanding I have trough Dutch only goes so far...

There should really exist a linguistic description of the ei->a shift that gave us Gas instead of Geiss. Finding this in the literature would help us a lot.