10.27. Using diverse data sources is crucial for a comprehensive system that facilitates the collection of travel-related transactions made by residents abroad and by non-residents in the compiling economy. One of the main challenges in designing a compilation system for the travel item is the integration of different data sources with different degrees of coverage and different periodicities and that may contain overlapping data. There is a trade-off between reducing the impact of possible double-counting and covering the various types of expenditures of travellers as much as possible. The extensive detail of the payment card database could allow the compiler to mitigate that risk.
 Recently designated as issuer identification number (IIN).
 For that purpose, correspondence tables between national industrial or activity classifications (e.g., between Statistical Classification of Economic Activities in the European Community (NACE) or merchant category code merchant category code (MCC)) and travel expenditures on goods and different types of services should be developed.