What is the difference among その上 and 上に?


Could somebody explain me the difference between その上 and 上に?

In "A Dictionary of Intermediate Japanese Grammar" it is written that they can
be used interchangeably, but I am not sure if it meant that they are always
interchangeable or that there are cases where they can be used indifferently.




その上 is a conjunction that means "in addition (to that)", so it is used like
私は英語が得意、その上、絵も上手.

A noun 上 has many meanings and 上に is "a noun 上 + a particle に".
<https://dictionary.goo.ne.jp/jn/17464/meaning/m0u/> So there are many usages
of it.

You can say 私は英語が得意な上に、絵も上手. This meaning is the same as 私は英語が得意、その上、絵も上手.

