Final answer:
Approximately 40-50% of the southern population were members of slave-holding families.
Step-by-step explanation:
According to a map issued by the US Coast Guard in 1860, the percentage of slaves in the population varied across the southern states. The map shows that in some counties, around 47% of the population were slaves, while in others, around 39% were slaves. Based on this information, it can be concluded that approximately 40-50% of the southern population were members of slave-holding families.