"I have been given it on the condition that I do not pass it on." What does that mean?

Question

I was reading an article from The New Yorker and I came across one sentence that I couldn't really understand.

The map runs to sixteen laminated foolscap pages, or about ten square feet, when I tile the pages together. I have been given it on the condition that I do not pass it on. It is not like any map I have ever seen, and I have seen some strange maps in my time.

Is there anybody that could help me to explain/rephrase the second sentence so that the structure or the meaning could be more lucid to understand?

Here's the link for the original article. https://www.newyorker.com/news/dispatch/the-invisible-city-beneath-paris

Answer 1

I have been given it on the condition that I do not pass it on.

The person who gave the author the map made the author agree to a condition. The condition is that the author of the article cannot pass the map on to other people (give it to other people.)

"On (the) condition that" is a set phrase meaning something happens only if a condition is met.

Merriam Webster:

only if

She spoke on the condition that she not be identified.
He taught me the trick on condition that I never tell anyone else how to do it.