  The urban spatial structure represents the distribution of public and private
spaces in cities and how people move within them. While it usually evolves
slowly, it can change fast during large-scale emergency events, as well as due
to urban renewal in rapidly developing countries. This work presents an
approach to delineate such urban dynamics in quasi-real-time through a human
mobility metric, the mobility centrality index $\Delta KS$. As a case study, we
tracked the urban dynamics of eleven Spanish cities during the COVID-19
pandemic. Results revealed that their structures became more monocentric during
the lockdown in the first wave, but kept their regular spatial structures
during the second wave. To provide a more comprehensive understanding of
mobility from home, we also introduce a dimensionless metric, $KS_{HBT}$, which
measures the extent of home-based travel and provides statistical insights into
the transmission of COVID-19. By utilizing individual mobility data, our
metrics enable the detection of changes in the urban spatial structure.
