The analysis of the event attendance used data scraped off the Sanders campaign website. With the help of Jeremy Bowers, our colleague in the New York Times Washington bureau, we grabbed the ZIP code, county and state of Sanders events, including the number of people who RSVP’d online to each event. More than 100,000 people were registered to attend.

The pattern of Mr. Sanders’s support resembles Mr. Obama’s support from 2008, but with nearly no support from the black voters who decided that election in Mr. Obama’s favor.

Mr. Sanders’s challenge among nonwhite and conservative voters has been widely reported. But the geographic concentration of Mr. Sanders’s activist base is striking even in the context of those expectations. While more than a thousand people showed up to Sanders events in Seattle, San Francisco and Portland, Ore., there were equally populated Southern and nonwhite areas where there were no Sanders events at all. His top 15 congressional districts, each with at least 750 registered attendees, were all in Oregon, Washington, California — or Vermont. Next came Boulder, Colo.

The South was Mr. Sanders’s weakest region: Mississippi, Georgia, Louisiana and South Carolina all sat at the bottom of the list. The turnout for Mr. Sanders — measured by comparing the number of RSVPs with the number of Obama voters — was 12 times as great in Oregon as in Mississippi. There were more attendees in Washington than in the far larger state of Texas.