On one of the busiest street corners for the meth trade in San Francisco, buyers and sellers barely make an effort to conceal their transactions.

Users palm drug packets after paying in cash that is quickly pocketed. Some don't wander far before using.

Sixth and Minna streets appears to be ground zero for methamphetamine deals in San Francisco, according to San Francisco Police Department incident reports. Not surprisingly, police presence in the area — roughly between Jessie and Natoma streets — is a constant. It's not unusual to see officers fitting someone for handcuffs.

Among hard-core drugs, meth is king in San Francisco, at least in terms of police interdiction. There were 755 meth-related incidents from Sept. 2016 through August 2017, nearly double the incident reports for heroin and crack cocaine combined.

San Francisco software engineer Katie Hempenius wanted to find out which street corners foster the narcotics trade in the city, so she created heat maps based on SFPD data regarding drug-related incidents.

"Given how visible the narcotics industry is within San Francisco, I've always been curious about how it operates — in particular how it varies from block to block," she wrote on her blog.

What she discovered won't surprise those who frequent streets east of the the Civic Center — the Tenderloin and the Sixth street corridor south of Market are hubs of the drug business.

Hempenius notes that law enforcement interaction with the street-level narcotics trade is not a perfect indicator of all drug activity. Drugs can be obtained from sources other than suppliers on the street.

The SFPD data showed only one other area in the city had a significant level of narcotics activity (in terms of sample size) — 16th and Mission streets near the BART station — but it did not match the activity around the Civic Center.

Officers logged only 70 incidents related to non-heroin opioids such as fentanyl and other prescription pain relievers, making it difficult to draw any conclusions about opioid abuse in San Francisco. Again because of the small sample size, Hempenius decided not to map the incidents.

The above gallery shows San Francisco's busiest meth-, heroin- and crack cocaine-trafficking intersections.