What are the usages of のだから?


I'm reading a book and I came across a usage of のだから I couldn't really
understand.  
The whole sentence is:

> その上に[無慮]{むりょ}百に及ぶ階層が積み重なっているという`のだから`、[茫漠]{ぼうばく}とした広大さは想像を絶する。

My translation to it was : "It has been said that on top of that, about 100
levels are accumulating (on top of each other), and therefore, its vast size
is unimaginable". Obviously this is not a literal translation.

What I don't get is the role that `のだから` plays in this case.  
I'd say it has a nuance of cause/result, but then why ので・から were not used in
this case?

According to the "best" answer in [this
question](https://japanese.stackexchange.com/questions/1870/%E3%81%AE%E3%81%A0%E3%81%8B%E3%82%89-vs-%E3%81%AE%E3%81%A0-%E3%82%93%E3%81%A0%E3%81%8B%E3%82%89-vs-%E3%82%93%E3%81%A0%EF%BC%89),
のだから has 2 rules:

  1. Used when both the speaker and listener know some fact, but expresses a strong feeling on the part of the speaker that the listener, although conscious of said fact, does not fully appreciate its implications.
  2. The clause following ～のだから often expresses the speaker's judgment, intent, wish, or request.

I know for sure that rule (1) is not true in this case, since the fact given
in the first part of the sentence was never previously mentioned in the book.

As for (2), I'm still not sure whether the part that comes after のだから can be
counted as a "judgment"...

Hopefully someone can help me grasp the idea of のだから!  
Thanks in advance!

I'd also appreciate even a list of all of the variations の・ん＋です・だ, so I could
at least research them myself as I always tend to get confused with them... a
link or a short summary of them would be even better but it's really too much
of me to ask!

Also, if you want to know, the sentence above was taken from the book
ソードアート・オンライン１－アインクラッド。




I interpret the の in your example as a nominalizer and shows that this clause
is explaining something else in the text. 「なんで腹が痛いか？」「アイスを食べすぎたのだ」.

It's the difference between saying:  
"Additionally, it's said about 100 layers have accumulated, so (から) its vast
bulk is unimaginably large."  
_and_  
"Additionally, because it's said that about 100 layers have accumulated, its
vast bulk is unimaginably large."

Sometimes, の is just a nominalizer, but it seems to me that if you find it
near the end of a sentence, it's going to connote either asking for
explanation (腹が痛いの？) or providing one (アイスを食べすぎたのだ).

Edit: I feel silly for having answered this a year later, but it was near the
top of the list when I checked and I didn't think to look at the date stamp
until I posted. Alas.




As a native Japanese speaker, I do not find a grammatical parsing of 「のだから」 or
「というのだから」 to be of much value or help to understanding its role in this
particular sentence because it is being used as a set phrase.

「A + というのだから + B.」 expresses:

> "Since they say A, (which was unexpected, surprising, etc.), I now must
> conclude that B."

The 「というのだから」 in this sentence can be replaced with 「というから」 to retain the
exact same meaning but with a slight difference in nuance. The latter is used
more often than the former. The former sounds more emphatic than the latter.

You will often hear us say things like:

> 「～～というから[驚]{おどろ}きだ。」  
>  「～～というのだから[大]{たい}したものである。」

