"The river behind the city is wide and deep."
Translation:A folyó a város mögött széles és mély.
Would it mean the same thing?
I understand A város mögött a folyó széles és mély as "Behind the city, the river is wide and deep." The "behind the city" bit just serves as an aside to set the scene for what we are talking about.
But the English sentence "The river behind the city is wide and deep" (with no commas) says that of all the rivers in the world, I am talking specifically about the one that is behind the city. And this river behind the city is wide and deep. So like Az a folyó széles és mély, amelyik a város mögött van. or something like that.
I assumed that A folyó a város mögött means the same thing (restrictive clause, not non-restrictive clause).
A város mögötti (a?) folyó I would understand as well.
But A város mögött a folyó doesn't sound to me as if a város mögött is talking about the river in any way.
No, "a folyó a város mögött" and "a város mögött a folyó" are not very much different. It is mostly just an emphasis thing. Although one could argue that the first one might identify the river as "the one". But that is very ambiguous at best.
If you want to clearly identify the river, then you can use the structure you mention:
"A város mögötti folyó" - the river that is behind the city
There is no extra "a". Think of "város mögötti" as an adjective structure:
"A hosszú folyó"
"A város mögötti folyó"
This "A város mögötti folyó" is the much preferred and simpler alternative to "(az) a folyó, amelyik a város mögött van". It is not always possible to substitute one for the other, but here it is possible.
"A város mögötti folyó"
"A város mögött levő/lévő folyó" - "being behind the city"
"A város mögött található folyó" - "can be found behind the city"
Ah, so in a város mögött a folyó, the a város mögött does kind of "stick" to the a folyó, modifying it?
I was not expecting that, but that would explain it.
I am not sure what you mean exactly, sorry. But my feeling is that I am saying the opposite.
We have "the river", which is definite, so we already know which river we are talking about. And this river is wide and deep behind the city. Both
"A város mögött a folyó" and
"A folyó a város mögött"
are closer to this interpretation. They may try to identify the river but that is vague.
Then we have
"A város mögötti folyó",
which definitely identifies the river as the one being behind the city. Just as "the long river" would do.
I have seen both "és" and "vagy" used to mean "and", but I don't know when to choose one or the other. My sentence "A folyó a város mögött széles vagy mély." was considered wrong.
Vagy is "or". Your sentence means "The river behind the city is wide or deep."