By the time two gunmen opened fire inside a San Bernardino social service center on Wednesday, killing 14 people, another mass shooting had already happened that day.

Earlier that morning, in Savannah, Ga. a gunman shot four people, killing one woman and injuring three men. The underreported incident underscores the bleak reality of how routine mass shootings are in the United States.

To date, there have been 337 days in 2015 and 354 mass shootings, according to the Mass Shooting Tracker, a site that tabulates incidents based on crowdsourced news reports submitted by reddit users. That's more mass shootings than days of the year.

In its count, the tracker uses a broader definition than some other databases, defining a "mass shooting" -- based on an old FBI classification -- as an incident in which four or more people, including the gunman, are killed or injured by gunfire.

The number of mass shootings this year has already eclipsed last year's total of 336, and is nearing the 365 incidents in 2013. The vast majority of perpetrators are young, white men.

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Perhaps most shocking, however, is that despite the heightened public attention that large mass shootings generate, these incidents only account for a tiny fraction of total U.S. firearms deaths and injuries each year. To date, 465 people have been killed this year in mass shooting incidents, according to the tracker site. Compare that to the more than 33,000 gun deaths in 2013, the latest year that Centers for Disease Control and Prevention data is available. Roughly two-thirds of these are suicides.

The three maps below, all based on the same data set from the Mass Shooting Tracker, show every recorded 2015 mass shooting to date tabulated by the site.

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MAP: Every "Mass Shooting" in America So Far This Year

MAP: Every Mass Shooting in America This Year (So Far)

America's Mass Shooting Dilemma