What drug poses the greatest threat?

This map shows how local law enforcement answered the question, "What drug poses the greatest threat to your area?" Blue is cocaine, red is methamphetamine, amber is heroin, and green is marijuana.

This map is from the National Drug Threat Survey. Even though I'm aware of the regional differences in drug use, it's still striking every time I see something like this. I'm surprised that there were not more mentions of heroin.
[hat tip: Addiction Inbox]