My daughter Rachel came across the world mapped by whether people drive on the left or right. Driving on the left does seem to be a British imperial legacy, though I remember hearing in England that it was based on ancient traditions. Swordsmen, my friends explained, would want to pass on the left in hostile circumstances, to keep their sword arm ready for defence. There’s a huge amount of information about this on the web (some of it backing up the swordman explanation), and it is interesting to imagine the chaos of border crossings where the rules change.
It’s one of the things that it really might make sense to standardize internationally. I’ll campaign for that after the USA switches to the metric system, okay? I actually had someone tell me that they couldn’t understand why America was so backwards–using pints and inches in this day and age. Let’s start there. I’m longing to be able to use A4 paper.