In my head, a recreation ground (or a school/college) has facilities which include playing fields. However, playing fields may also exist on their own. Playing fields contain one or more pitches. As part of a more formal recreation ground or other sports centre, pitches tend to be well laid out, painted and have nets on the goal posts. More often than not, standalone playing fields have little more than 2 sets of goal posts facing each other across some grass.

It's worth mentioning that "thee"/"thou" is not just the Yorkshire version of "you". It's more like using "tu"/"toi" in French in that it implies familiarity. "You" is comparable to "vous" in that context. I remember this in the context of a teacher who started work at a school in Barnsley. The children theed and thoued, which he found charming. It wasn't until after a few weeks had passed, that it was explained to him that they were being rude. :)

This distinction is why I find the second phrase clearer. It is explicitly the mode of travel to London. "Grouped by" is very frequently shortened to just "by" in charts and diagrams, so for me, the addition of "grouped" is redundant and in the context of an annotated diagram, less text is generally better.

@ElliottFrisch - Interesting point on "plied". It would make sense given that the origin of the word seems to be the French "plier" (to fold), and the verb "replier" means "to refold".

Now I'm curious about whether any other languages do have more tendency to define reciprocal relationships between actions and consequences. Although I guess that's off-topic around here. :)

To be honest, it's a bit more hypothetical than that. It's just something I got to thinking about when trying to describe relationships between letters, telegrams, emails, etc. For instance, if B is a "reply" to A, then A is a "???" to B.