In NYC fpr example when you get off the train and come up to the street level many times you don't know what east west uptown downtown is... I mean if you are standing on Brodaway and 42nd street and look up the block and see 43rd street as the next block than pretty much you know what your body position is. But chances are that you won't be able to see it (rain, obstruction, snow, stolen sign), or numeric streets change into names which in this case can confuse you. You can't do similar check up with the avenues becasue they are spaced to far appart. If you have a compass it's pretty much clear where you are all the time.
Matt