I thought what if there was a flag for the Iberian Peninsular? Perhaps for a political union, or for a monetary union or joint sport team or even just as a geographical flag?
I admit I am not the first person to think about this, and quick search on YouTube will find flag designs for both fictitious states and alternative history. Here are a few of my favourites:
This flag for a fictitious state, possibly inspired by the UK Flag, combines the early flag of Portugal, with what appears to be a saltire cross in the Spanish colours probably based on the cross of Burgundy. Both the Spanish and Portuguese coat of arms (including the supporters) are combined.
This flag combines the Current Spanish flag, with the flag that was used by the old Portuguese Monarchy. Again the coat of arms are combined but with the Portuguese shield being placed in the centre. The use of the old flag of Portugal and use of the crown suggests this alterative history state is a monarchy.
Some flags are/were used by the Iberian Federalism movements, which also use the colours of spain and the old Portugal flag:
This flag of Iberia was created by a Catalonian diplomat in 1854, although it has no official status in any country it is technically older than the current flags of both Spain and Portugal. Despite the fact it is a little outdated supporters of Iberian Federalism continue to use these colours today. Personally I don't like it, it looks like some sort of signal flag and reminds me of the House Flag and Jack of the ship company P&O :
Which is no coincidence as in its early days the company initially sailed ships between England and Spain an Portugal.
Personally I think the best flag I saw and the one I am going to base my proposal on is this:
It combines the current flags of the two countries, it also combines the coat of arms two.
My design is based on this but only using the shield of the coat of arms:
Normally I don't like putting coats of arms on flags but without one I don't think the flag works as well without it. I left out any monarchist or republican symbols so it would be acceptable in a non political context like sport. Perhaps an alternative to the arms are two stars representing the two countries:
Stars I think are more neutral in any kind of environment as coats of arms seem to suggest a political union, where stars allow it to be used in sport, or simply in a geographical nature.