If you have a lot of Facebook friends on the coasts or in the Great Lakes region, you might remember many of them changing their profile pictures to an equal sign against a red background in late March.

It was part of a Human Rights Campaign social media effort to promote gay marriage, and 2.77 million Facebook users in the United States joined in, according to the social network. But there were differences depending on geography and age, according to analyses of the viral campaign. Those on the coasts and in the Great Lakes were more likely to change their profile pictures to the Human Rights Campaign graphic or an equivalent. But users in the South or in the Great Plains regions of the country were less likely to have joined the effort, according to a Facebook post analyzing the effort, a follow-up to another conducted right after the campaign.

HRC began urging its members to change their photos around 1 p.m. Monday, March 25, according to Facebook. There were some variations in the image used, but the social network’s scientists wrote some code to catch those. The rate at which users update their profile photo rises and falls over the course of a week, but the chart below shows that updates spiked significantly after HRC began its push—signified by the dashed line.

Thirty-year-olds and women updated the most

Those closest to age 30 showed the biggest uptick in profile updates. A Facebook data scientist estimates that roughly 3.5 percent of 30-year-olds changed their photos, on average. And adoption was slightly higher among women than men (2.3 percent v. 2.1 percent).

Counties with college towns saw higher participation

The initial study of the social media campaign found high adoption rates in college towns. The highest rate anywhere was in Michigan’s Washtenaw County, home to Ann Arbor and the University of Michigan. About 6.2 percent of users there logged in and changed their profile photos for the campaign. Other counties in the top 25 that were also home to colleges or universities included “Orange (University of North Carolina), Durham (Duke University), Monroe (Indiana University), Johnson (University of Iowa), Athens (Ohio University), Dane (University of Wisconsin), Boulder (University of Colorado), and Travis (University of Texas at Austin).” San Francisco County, San Mateo County, and the District of Columbia also had high adoption rates.

Participation varied—greatly, in some cases—within cities

While many cities saw high rates of participation in the campaign, the new analysis shows that there was in some cases great variation within cities.

“These striking differences at the level of urban areas could be the either the result of large geographical differences in terms of support for marriage equality, or they could be the result of lack of connectivity between social networks that made the phenomenon less likely to catch on in certain regions,” Facebook’s Bogdan State and Lada Adamic wrote  Monday afternoon.

In New York, adoption was highest in Manhattan and the parts of Brooklyn and Queens closest to it. But the rates of people changing their profile pictures were very low in the Bronx, outer Brooklyn and Queens, parts of Long Island, Staten Island and New Jersey.

Participation was higher in northern Chicago than in the south of the city.

The northern and western parts of Los Angeles saw high rates of participation, while fewer users in Compton, Orange County and San Bernardino County joined in.

In the San Francisco Bay Area, participation in the campaign was high almost everywhere. That result isn’t surprising, given the region’s large gay population and iconic status in the history of gay America.