Centro vs. baixa
When referring to the heart of a city, the choice between centro and baixa largely depends on regional usage—specifically between Brazil and Portugal—and the specific layout of the town. While centro is a universal term, baixa carries a specific historical and topographical weight in European Portuguese.
Centro
A1Centro is the most common and neutral way to say city center or downtown in all Portuguese-speaking countries, including Brazil and Portugal. It refers to the central business district, the administrative hub, or the geographic middle of the city.
Eu trabalho no centro da cidade.
(I work in the city center.)
O trânsito para o centro está muito complicado hoje.
(Traffic toward downtown is very complicated today.)
Nós vamos jantar em um restaurante no centro.
(We are going to have dinner at a restaurant downtown.)
Ela mora bem no centro de São Paulo.
(She lives right in the center of São Paulo.)
Baixa
A2Used primarily in Portugal, baixa refers specifically to the historic, traditional commercial district of a city. The name literally derives from low, as these areas are historically located in the lower valleys or near the waterfront, distinct from the residential neighborhoods located on the hills.
Vamos passear na Baixa de Lisboa esta tarde.
(Let's go for a walk in downtown Lisbon this afternoon.)
As lojas na Baixa fecham às sete da noite.
(The shops in the downtown district close at seven in the evening.)
Os turistas adoram a arquitetura antiga da Baixa.
(Tourists love the old architecture of the historic downtown.)
É difícil encontrar estacionamento na Baixa.
(It is difficult to find parking in the lower city center.)
Summary
In summary, use centro as a safe, universal term for downtown in any Portuguese-speaking region, especially in Brazil. Use baixa specifically when you are in Portugal and referring to the historic, often lower-lying commercial heart of a city like Lisbon or Porto.