The simple answer, if the same criteria apply as they did when I was last at Raleigh, is that there are roadways and tarmac pathways, in between which are landscaped areas, mainly laid to grass. The RN does not like to continually state the obvious, but also does not wish it's nice green lawns to be transformed into a quagmire by hundreds of pairs of parade boots stomping all over them whilst seeking a shortcut. Since the current yoof seems to be incapable of appreciating anything of beauty, such as a nicely laid lawn, without wanting to play football, or skateboarding, or something similar, on it, it will be pointed out to them on entry, that transgressing onto grassed areas in HMS Raleigh will not be appreciated, and will thereafter be discouraged. This, in rough translation, will be heard as:-
"GET OFF THAT F*%K!^ GRASS AND REPORT TO ME"
2BM