While early voting continues Monday in some places, and absentee ballots in some states will be accepted after Election Day, the totals visualized here lay out the best picture available of how the nation voted early.

This data, collected by associate professor Michael McDonald at the University of Florida in conjunction with the AP, is one of the most comprehensive sources for early-voting tallies across the country.

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As we mentioned in a previous graphic, the completeness of these figures hinges on how quickly the state office administering the election can process returned ballots.

The steps of “collecting these data are a real challenge, especially if the state doesn't have a centralized reporting system,” McDonald said. He estimated a third of states don’t have a centralized system that makes detailed voting data publicly available.

Sunday’s totals were about 5 million votes short of the 2012 total, but McDonald attributes that difference to incomplete reporting from state election officials at this point in the campaign.

“I'm confident that we will exceed the national total number from 2012,” he said in an email Sunday.

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Another reason for low early vote totals in several states: A handful, including many in the Northeast, had little advance voting because they require a reason to vote early, such as military service or being unable to visit your polling place on Election Day.

But in some states, early voting has become the norm. Over the last 30 years, Western states have changed their voting laws to accommodate more convenient voting methods. In three — Oregon, Washington and Colorado — all voters will get ballots by mail in 2016.

Some findings from early voting data: