Particle Use When Using Form V-ている/ある at a Location: で or に?


So imagine I get asked this question, perhaps when calling someone:
図書館...何をしている。 Perhaps I am reading a book, so: ［僕は］としょかん...本を読んでいる。 Here is
the problem. For "...", I am conflicted on whether to use で or に in each
instance and in general. I know that being at a location is に, and doing an
action at a location is で, but what of this sentence pattern? Are there
specific cases for whether to use one or the other?




You are talking about some action that is taking place in the 図書館, so you have
to use で.

> 図書館 **で** 本を読んでいます。

  * [Particles: に vs. で](https://japanese.stackexchange.com/q/60/5010)

There is a subsidiary verb いる used to express progressive "-ing", but it
doesn't interfere with this rule.

