Hi Alberto,
Conditionally updating (dynamic) filters are not possible to create yet. It’s a planned feature, but it will probably require 4-6 months of development in order to work properly. (unfortunately it’s very complicated to make it usable in all cases)
“all locations” option
For that, all you need is an empty value to the list: https://goo.gl/vVwCqH
Something like:
[code]
||Any Location
North West||North West
North East||North East
South West||South West
South East||South East
[/code]