Centrality depends on jobs, but not exclusively. In 2009 most of the census blocks in Madrid had less workers in the firms on site than residents registered in the municipality; it is pertinent to remind that the census block is a zone defined for population censuses, and so their area varies, being much larger on rural or industrial areas, with small permanent populations.
The balance between jobs and residents has been an obsession of planning for much of the last decades, as it could help optimize the mobility systems and public facilities, and to avoid monofunctional neighborhoods; in countries deemed to be advanced, where the job history of each citizen is becoming less uniform and stable, this is becoming harder. Despite that, an indicator of centrality of a zone can be the ratio between workers and residents up to a certain point; too many workers and you loose diversity, or you are entirely in a single function space, as industrial areas.
In central Madrid there is a clear north-south corridor with many sections in which there are more than 3 jobs per resident; a large part of the Barrio de Salamanca and the surroundings of Gran Vía were in that condition. The analysis of the census blocks of the whole region show the highest values in industrial areas, the Barajas airport (1), the rail yards of Atocha Station (2) or the University City (3), mainly monofunctional spaces. There is also Azca (4), an attempt from the 1960 to configure a sky-scrapers area, and the surroundings of Cibeles and the Bank of Spain (5) with many public and private institutions; in this cases the census blocks are somehow moderate in size, and they are inserted in a more populated environment, without physical barriers, and accessible by all means of transportation, so they definitely are central.
Inside the M-30 beltway the average value in 2009 was 0,85 jobs per resident.