Currently there are already several Portuguese and Japanese twin cities that have established formal relationships with each other. The best known for formal relationships between cities form is twinning with each other:
Town twinning is a concept that aims to create relations and protocol mechanisms, primarily the economic and cultural level, through which cities in different geographical or political areas, establish cooperative ties.
In Europe they are called twin or twin cities, while in Brazil and the US normally call “sister cities.”
Generally, the twin cities have similar characteristics (demographic, for example) or points and common historical references.
This concept is similar to the practice of correspondence in the worldwide network, where the pals are cities or towns as a whole. These agreements lead to the establishment and cultural exchange, knowledge sharing, teaching (students) and corporate policies and other activities.