City of Melbourne — Landor
This is probably the most famous recent city rebrand, with a flexible brand system. A grid system that creates the logo has been applied over the entire identity, making the brand both fun and playful, but also consistent.
Porto — White Studio
I like the playfulness of this graphic system. The tiles allow flexible use, with endless possibilities.
Personalised icons have also been used to show different aspects of the city.
Latvia Expo 2010 — Asketic
Although i'm not keen on the aesthetic, I like the overall system used. As you can see, the use of simple shapes allows a flexibility within the brand, as seen in the use of patterns and multiple logotypes.
Alenquer — Miquel Palmeiro
Here you can see a logo mark which has an adaptable form. The different additions are used to show something unique to the region. This could be used to highlights unique things different northern cities are known for, or have to offer other cities.
Vila do Conde — Monica Pereira
Although the design for the above project is not too too complex, I like the concept behind it. It's clear that the city has many arches, so the designer has used the buildings architecture to summarise the city. This could be done for the major northern cities if they have clear differences.