Translation:The police station is not far from your library.
Shouldn't this be "nem messze van" instead of "nincs messze"?
It is not about is/isn't, but where it is: far/not far?
And it is "not far from your library" / "nem messze a könyvtárataktól"???
The reverse: The police station is far from from your library.
A könyvtárataktól messze van a rendőrség.
And now we negate far and not is???
As it is the Hungarian seems to mean:
There is no police station far from your library. ? i.e. If there are police stations at all, they are all near your library. ???
As I understand it, the negative of 'van' is always 'nincs'. It doesn't matter if we would translate 'van' as 'there is' or just 'is' or even 'have', the negative is always 'nincs'.
Also, I don't think it helps to think of negating the adjective. It's the verb that is negated: 'The police station [is not] far ...' rather than 'The police station is [not far] ...'
Don't think about van/nincs as meaning 'there is/there isn't' in this context. When it's with messze we would just translate 'van/nincs' as 'is/isn't'
Messze van = it is far
Nincs messze = it isn't far
(native or more advanced Hungarian speakers, please correct me if I'm wrong!!)