From a macroeconomic point of view we are especially interested in the share of euro cash in circulation, which is used for domestic transactions in the euro area, since this is a key variable for measuring economic activity and price developments.
First, big/web data might lose their statistical relevance when they are employed in an unsound way. Such data typically entail selection bias because of the features of the population; increasing  See, for example, ‘Big data processing: Is there a framework suitable for economists and statisticians?’, 2017 IEEE International Conference on Big Data (Big Data), 2017, pp. 2804-2811, doi: 10.1109/BigData.2017.8258247.