Difference between って and は as topic marker


I often see って being used to mark a topic, such as in the sentence 新宿ってどこ？ I'm
aware that this is more colloquial compared to the topic marker は. Other than
the formality aspect, are って and は completely interchangeable in meaning when
used like this?




は is fairly matter of fact. "Where is Shinjuku?"

って is a little more nuanced. Its like "Oh, now that you mention
Shinjuku...where is it?" or "Speaking of Shinjuku, where is that?"

For all intents and purposes I gather the actual end-point meaning is the same
but って is linking it more with something that has been previously said whilst
は could just be bringing it up out of the blue. I feel that because it has
this prior link it comes across as less forceful, just like such a situation
in English.

