As a nation we like rankings. We rank all kinds of things: Companies, cities, television sets. Usually, the reasons for a particular ranking are clear. Companies are ranked by revenues, cities by the number of jobs and hospitals they have, and television sets by the clarity of their picture.
But when it comes to payment card transaction processors, the picture is anything but clear. A few publications print rankings of the largest card processors, but the companies themselves dont agree on much when it comes to deciding exactly how they should be ranked. Processors favor several different measures of transactions, not surprisingly usually settling on the one that makes their performance look better.