Quite.

I’ve been rather liberal about the extents of Zones 1 & 2 so far¹ but, really Zone 3 is everywhere north of the River ², everywhere south of Streatham, everywhere west of Battersea and everywhere east of Brixton

But, no, actually … further afield even than that — beyond ‘Zone 9’ in fact and into the wilds of …

It was a most disconcerting experience, I must say — when I’ve recovered from the horror of it all, I might be inclined to write about it.

—
¹ https://medium.com/@WhereAngelsFearToTread/zone-3-cf057862d5d0

² Please note the use of the capital letter there (something you singularly failed to employ); it is the River, not merely a/some river and, therefore, requires a capital, just like any other proper noun (C.f. the South, the Sun, the Moon, the Earth, etc.) — obviously, that only applies to the Thames, not the rivers in Zone 3 ³.

³ Which don’t require names, as nobody from anywhere else cares where they are, let alone what they’re called.