According to socrates, does he need to prove that his theoretical city can actually come into being exactly as described?

I believe this question deals with Book IV of "The Republic." Gradesave has a complete summary and analysis of this book. Check out the link provided below.

http://www.gradesaver.com/the-republic/study-guide/section4/

If this is not the correct section, please let me know.

yes i do think he has to explain because a city does not just change in a day

who cares?