The comparative maps show the number of credit card transactions in Barcelona performed by locals (blue) as well as visitors (pink). It displays data from the week before (left) versus the week during the Mobile World Congress in February/March 2012 (right), in order to reveal the social and economic dynamics of this event in the city.
This interesting dataset from Spanish bank BBVA includes all credit card transactions of its own customers, as well as any transaction that is recorded through its payment devices, and this for the whole of Spain. Notably, it has been visualized before by the MIT Senseable City Lab. The data has been wholly anonymized, and includes only where and when transactions were performed.