As you are aware, English has two meanings of 'about' - as in:
1. 'about' = 'approximately
2. 'about (something) = 'pertaining to/having to do~ with something'
Japanese makes this distinction by using entirely different expressions.
When you want to say _'about'_ as in, _'approximately'_ you can use the ending *~gurai/~kurai*.
:idea: *~gurai* (or *~kurai*) after a number or quantity indicates it is an approximation: _'about~ / ~or so'._
It is often used when referring to time - so, _'about 1pm'_ would be *'Ichi-ji gurai'*.
When you want to refer to something - such as *Nihon tēen*, Japanese Garden, and talk about that, you attach the phrase *~ni tsuite*. So *Nihon tēen ni tsuite...* translates as _'about the Japanese Garden...'_ in English in the sense of _'pertaining to the Japanese Garden.'_ In this case, _'about'_ does not mean _'approximately'_.