The rank size rule is valid for Portugal in most cases. The estimate of the second largest city and the actual population of Porto is only about a 39,000 people difference. the estimate of the third largest city is only about a 2,000 people difference from the actual population of Villa Nova de Gaia. The estimate of the fourth city and the actual population of Amadora is a large difference and the actual population is closer to the estimate of the third largest city. The fifth largest city is closer to the estimate of the fourth largest city than the fifth largest city.