The Köppen–Geiger climate classification made simpler (I hope so)

[Charerg]

As far as I am aware, the 0 vs -3 is not something climatologist agree on. I picked 0 because (Pixie probably) it makes more sense since it's the freezing point.

I'd say -3 is probably the better one since it pushes a lot of maritime and montane climates from Dc into Cc (Iceland, the Southern Alps, much of the southern Andes). But you still need the 0 °C in any case because it's the boundary between EF and ET, so using -3 °C would require adding a new temperature category (and a very narrow one too, being only from -3 to 0 °C). In that sense, using 0 °C is probably more practical, unless using some other method to create the temperature map (like creating a gradual greyscale map and then converting it into temperature zones instead of painting the zones directly by hand).

Though apparently the current model puts the Icelandic coast and the Southern Alps as Db (they should be either Cc or Dc depending on the isotherm used). I guess one way to fix that would be to split Mild (10-18 °C) into two categories, so the Cc/Dc could be more accurately separated from Cb/Db, but again that would require an extra temperature category (and again, probably quite narrow, maybe 10-14 °C would work).