This is late, but I think it's basically the difference between zone and region in English. A region is an area that's often large and constitutes places of similar characteristics, and zones are smaller restricted areas with certain purposes. Zones are often in regions.
Many of the words that end in -ion in French and Spanish are feminine. Is Portuguese like this?
Generally, if the word that ends in -ão is an abstract noun, then it's feminine. If it's a concrete noun, then it's masculine. There are also words that have masculine and feminine versions. They refer to people and animals.
People: anão/anã, cidadão/cidadã, alemão/alemã, etc.
Animals: leão/leoa, pavão/pavoa, leitão/leitoa, etc.