[lclanzi]

When region stratification is not active, the dashboard, metric plots and scorecards silently used the first region listed under experiment.stratification.regions. There was no way to choose a different one without reordering the list.

This PR adds an optional experiment.stratification.default_region setting so the region can be chosen explicitly:

experiment:
  stratification:
    regions: [icon, mittelland, berge, alpennordseite, alpensuedseite, jura]
    default_region: icon

[jonasbhend]

Hi @lclanzi. I see where you are coming from, but I wonder if we should think a bit harder about how to tackle this. My concerns are the following:

• The PR only implements it for regions (not init_hours or seasons). While I get that the situation is slightly different for these (as the default is all for init_hours and seasons, and we don't want to have an all region to avoid ambiguity), one could argue that making all 'default' stratification explicit would be useful.
• I quite like the current solution for its simplicity, but agree that it is not well documented. Could we just improve the documentation to clarify (which would be a much smaller change)?

Maybe we need other opinions on this...

[lclanzi]

I agree that this methodology introduces some inconsistencies with how season and init_hour are handled. I think the simplest solution is indeed to add a comment in the config clarifying that the first region in the list is used. Feel free to close the PR.