So if festival-goers walk out of the Blues Festival into, say, a nearby gastropub for a late-night libation, and they use their Mastercard, data on the consequent uptick in spending at nearby restaurants will be aggregated and reported. The data will, of course, be anonymized, but the city still will know whether you are an international or a domestic cardholder. And by looking at aggregated spending data from hotels, it should also be able to estimate how many attendees spent the night in the city.