With the end of the second open enrollment period for the Affordable Care Act, the enrollment leader is not California, the largest state in the country by population with an insurance marketplace budget of about $400 million. Instead, Florida -- a state where public officials have decided against using any public dollars toward enrollment -- led the way.

The Sunshine State boosted enrollment between last year and this year by about 600,000 people to 1.6 million total, attracting the attention of national groups focused on expanding insurance coverage. To them, the state’s own strategies, a well-coordinated and data-driven approach, made the difference. But there could also be other factors at play.

Unlike California, Florida isn’t running its own online marketplace of insurance plans, which means the state depends on the federal Healthcare.Gov and $6.8 million in federal grants to pay organizations assisting with enrollment and outreach. California gets to keep the revenue its exchange produces to fund outreach. The state's budget was $168 million for enrollment alone, which includes public relations, agents helping sign up beneficiaries, marketing and some administrative costs.

But an exact comparison between the two states isn’t fair, officials and experts say. For one, California expanded Medicaid, meaning a significant number of people entered the program for low-income adults instead of purchasing a private insurance plan through Covered California, the state’s health exchange, which offers subsidies and tax credits to help defray the costs of those more expensive policies.

In California, which signed up about 1.4 million people in private plans through the end of the official enrollment period, 650,000 people who were part of an earlier low-income health program would have qualified for a private policy with financial assistance but are instead part of the state’s Medicaid expansion, said James Scullary, a spokesman. “We feel like any comparison of the ACA impact in California must include both Covered California enrollment and those enrolled in [Medicaid] through the ACA expansion,” he said.

Florida also had a higher rate of uninsured people before the ACA, 19 percent compared with California’s 15 percent, according to Kaiser Family Foundation data from 2013. Florida also had fierce competition among insurers, which numbered 14 in total--four more than last year. That competition prompted intense outreach among plans, Jon Urbanek, senior vice president of the state's Blue Cross Blue Shield plan, told Kaiser Health News. By contrast, the number of carriers in California contracted to 10.

Still, the question remains how Florida signed up so many people compared with, say, Texas, which had a similarly high rate of uninsured people, a larger population and didn’t expand Medicaid but trailed Florida by about 400,000 enrollees.

The fact that Florida has more people clustered in several urban areas, whereas Texas features more geographic isolation, is a likely factor in the state's success. The way Florida used its federal grant support also matters a whole lot, said Jessica Kendall, who directs enrollment assistance for the national group Families USA. “You can find those factors in other states, but Florida was able to coordinate in ways that I haven’t seen elsewhere,” she said.

Total federal aid last year actually exceeded this year’s total by about $1 million, but it was also spread across eight different groups. The University of South Florida was one of those groups, but this year it oversaw all of the grant funding and divided the state into 12 regions, each with a formal association of local groups responsible for developing a plan, inputting data on enrollment and outreach progress, as well as appointments among assisters, known as “navigators.”

Places like the Miami area, which previously had a number of individually-funded groups, now had greater organization. At 756,137, the area as a whole led all other metro areas under Healthcare.Gov in enrollment, more than double the next-highest region, Atlanta.

Each of the regions was using mapping technology first developed last year in the Tampa Bay area but taken statewide this year. Broken into census tracts utilizing existing demographic and insurance levels, the map measured enrollment and outreach efforts in real time and was continually referenced in regular briefings among the regional coalitions. Each tract grew progressively greener depending on the level of outreach in an area -- appointments with uninsured people, events -- and progressively redder as enrollment increased.

That allowed each region to target resources better and make the best use of its time, said Jodi Ray, the project director overseeing grants out of the university.  “It’s very helpful for the projects in our communities, because part of the work that had to be done and the reason our grant has had good success is the engagement of [outside] partners, and you can’t do that unless you can tell them what was going on,” she said. “It’s not enough to have navigators out there.”

Another advantage was having local coalitions already in place that have worked on enrollment in programs such as Medicare Part D and the Children’s Insurance Program. “We already had a lot of that structure in place and we were able to build upon that,” said Melanie Hall, who developed the mapping tool as executive director of the Family Healthcare Foundation in Tampa Bay.