Living alone in France: what geography?

For long a marginal phenomenon, one-person households have, over the last fifty years, become a major component of the sociology of France. How do we explain why more people are living alone, in both absolute and relative numbers? Should we not take into account demographic, social, economic and spatial factors? Is the geography of individuals living alone mainly concentrated in the big urban areas, impacted by the residential and professional mobility of young adults, break-ups and the ageing of the population?