Population density and building age in Barcelona

A bivariate choropleth analysis of how building age and population density interact across Barcelona’s 1,068 census sections.

Barcelona’s urban form carries its history in its buildings. The historic core is dense and old; the outer ring is newer and more spread out — but how clearly does that pattern hold at the census-section level? This project combines building-age data from the Cadastre with population data from the municipal census, joining them onto the official geospatial boundaries to produce a bivariate map.

Data sourced from the Ajuntament de Barcelona Open Data Portal.

Result

The bivariate colour scheme encodes two variables simultaneously: building age (x-axis of the legend) and population density (y-axis). Dark blue-purple = old and dense; light grey = new and sparse.

Population density and mean building age across Barcelona’s census sections

Instead of looking at a single variable, I tried to combine two: population density and the average age of buildings across Barcelona.

What I found interesting is that looking at them together tells a more nuanced story:

• In the historic core there is a pocket of high density and high building age in Raval, less so in Ciutat Vella
• But there are also pockets of relatively old buildings outside the very center, with high population density. Poble Sec is particularly striking.
• There is also a stark contrast between the Eixample Esquerra and Eixample Dreta
• And some dense areas that are not particularly old, hinting at more recent urban development

So rather than a simple “old center vs new outskirts” narrative, the city feels more heterogeneous, shaped by different waves of growth and transformation.

Full analysis

The complete data pipeline — loading five geospatial datasets, merging them, computing quantile-based bivariate classes, and producing all visualisations — is in the notebook that can be downloaded here.