Thanks for your detailed explaintion.
Does this mean that there won't be any departmental elections in Lyon Metropole?
Are these territorial councillors only elected in Grand Paris?
It's difficult to find any literature in English or German on this topic.
I have some questions regarding metropolitian / intercommunal elections:
Is the Lyon Metropolitan Council election the only election of councillors to intercommunal structures which doesn't place concurrently with the municipal elections?
Yeah, because of Lyon Métropole's unique situation since 2015 of being simultaneously a department and an intercommunality. So Lyon Métropole's councillors are elected by constituencies that group several communes (outside of Lyon) or arrondissements (within Lyon), as opposed to the other intercommunalities, whose council's are elected based on the municipal election results in each individual commune. That means, in Lyon Métropole you would cast a separate vote for both your municipality/arrondissement and for the Metropolitan election. Whereas everywhere else you just vote once in your municipality and that determines the Intercommunality council results.
Does the bonus system add 50% of the seats to the winning party at electoral district level or at metropolitan level?
Similar to the Paris/Marseille/Lyon municipal elections - the bonus is at the constituency level. No bonus for being the first party across the whole Métropole.
How are territorial council members elected?
As in the intercommunalities (and equivalent...)? It depends on the type of collectivity. For a collectivity "à fiscalité propre" (ie with the ability to collect taxes by itself). Each commune has a certain number of seats that it sends to the council. Seats are allocated based on the municipal results within the commune. For the most part, this works in the same way as the municipal election, half the available seats for the winning list and the remainder divided proportionally. Although if the commune in question has a population of under 1000, then it will be the mayor (and eventually deputy-mayors who get elected).
In practice, over 90% of the population live in a collectivity "à fiscalité propre", but for non-tax raising ones, councillors are elected directly by the municipal councils themselves.