When I go walking on the moors and Dales and I happen across another walker, it is the convention to say hi!, hello! etc.....however if I go, say, shopping in Leeds I wouldn't say hello to anyone unless I knew them.

The reason is quite simple.

Up on the moors I may come across two or three people, whereas in Leeds city centre I'd probably encounter thousands of people....if I said hello to them all I'd either lose my voice or never get that Hugo Boss 'T' shirt I wanted for my holidays.....