Biggest Cities in Portugal

Huh?

Those are the only 3 I've even heard of.

Vila Nova de Gaia is a Porto's suburb and Queluz, Barreiro, Almada, Cacém and Amadora are Lisbon Suburbs. Both cities have very limited area compared with other European cities and that explains the low population. In fact, there's no division between Porto and the suburbs and the same for Lisbon.

A suburb of a city should not be considered a city. This is why Lisbon and Porto are strangled and ranking so low in terms of population. Of course that there should be exceptions, if a city has an historical background but the way I see this, much of this so called "cities" within Lisbon itself only emerged to give Lisbons unhabitants more beds. The city had a natural growth but for some reason only its core remained "Lisbon" while its suburbs achieved a somewhat identical status, equalizing the core that actually expanded in the very first place in order to give them life. What will happen next is that these suburbs can keep growing and by so they will easily surpass its main core in population and area. Another deal here is that despite their quick growth, these suburbs aint autonomous enough to develop their own core (despite being cities), so they will remain totally dependent on Lisbon. Which for me certifies how wrongly portuguese administration upgraded dorms to cities.

You should see the USA.