Great maps! I like them a lot,
I know about nothing of politics in the Açores islands. It seems that PS is strong there, winning in most of the urban parishes and in many rural parishes too. Leftist parties look rather weak, but I noticed that Bloco de Esquerda performed pretty well in the parish of Rabo de Peixe in Sao Miguel island (Ribeira Grande municipality). Some professors I had went to the Açores and showed us some photographs. I vaguely remember they told that Rabo de Peixe is one of the poorest localities of Sao Miguel. Apparently there's some fishing industry in the parish.
The Aliança won in a single parish of Sao Jorge island. One of the members of the alliance is the Monarchist Party. I am curious to know if said party is stronger in Açores than in mainland Portugal.
I guess this is caused by reconquista and granting big parcels to nobles?
If we go way back in history, there could be some truth on what you said, especially because almost 60% of the population live in the North/Center regions, already excluding Lisbon, but i believe the main reason is geography. The terrains in the North and Center are very mountainous, only the terrains along the Spanish borders are plains. The South region is a huge plain area, from the Tagus river to the Algarve. In fact, the red, in that map, denotes mountainous areas, while green denotes plain areas. In mountainous areas, the properties were smaller, while in plains they are bigger. Fun fact: Alentejo means "Beyond the Tagus".In Spain the lands immediately south of the Tagus are the plains of La Mancha. Large parts of them were granted to nobles and military orders during the Reconquista. Further south, in the Guadalquivir Valley (Andalusia) great plots of land were granted to the nobles too. That is the remote origin of the large estates in Southern Spain and I guess that was the case in Portugal. As you say geography can determine the size and the shape of properties. However, there is a big difference in the ownership structure between the two Castiles in Spain (both are great plains in their most part). In the the Old Castile (Castilla y León) prevails small property, while in the New Castile (Castilla-La Mancha) properties are bigger in extension. Even the size of municipalities is bigger south of the Tagus river...
