What does 18,000 shipping containers really mean?

This is the kind of communications challenge that shipping company Maersk were faced with as part of their efforts to help their business be better understood by consumers. They have a really good media section on their website which tries to use visual aids to bring home some of the data points around their business.

My favourite image was this one of an altered Time Square vista to try and bring that 18,000 shipping container number into perspective.
Mearsk photo image
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Maersk Global Media Centre