Su Jin mentioned a place that was actually the present S city. In the past life, there was the biggest and safest safe zone in the whole country there. The safe zone wasn't established from the beginning but started to take shape after a while into the apocalypse.
Su Jin had visited the villa district there in her past life and had a very deep impression of it.
The earliest occupants who were a few survivors and original inhabitants were not driven away by the safe zone, instead, that area was designated as a key protection area. It was said that it was because some big shot was living there.
At least before she died, the S city's safe zone was the most coveted one, without a doubt. So, Su Jin wanted to take her family there first, to get ahead of others.