The safety of a location depends on the safety of surrounding locations (if all locations are green around a location, it only lose 1% per night, but if a location around has low safety, it will add +1% )
So in short, starting building safety in a dangerous zone will be nearly impossible, better build it up from a safer spot.
I always have the entire map all green, but whenever I rest for a few nights suddenly 8 regions are in deep red again, it gets really tedious at that point