There Have Been More Mass Shootings Since Newtown Than You've Heard About (INFOGRAPHIC)

When 13 people died in a shooting rampage at the Navy Yard in Washington, D.C., on Monday, the story made front page news. Many of the mass shootings that have happened since the massacre of elementary school students and teachers in Newtown, Conn., last December didn't.

Infographic by Jan Diehm for The Huffington Post.

The FBI's definition of mass murder is the slaying of four or more people. There have been at least 16 such tragedies already this year where the victims were gunned down, but shootings related to drug or gang violence often get less attention than those perpetrated by a crazed gunman.

HuffPost combed through a variety of news sources, including Reddit's community-generated database of mass shootings, and came up with this graphic, which may be incomplete. Killing sprees that occurred in more than one location were counted, but mass shootings that unfolded over more than one day, such as the string of homicides committed by ex-cop Christopher Dorner in Los Angeles, were not.

This is just one small and somewhat arbitrary measure of gun violence, but it shows that mass shootings have become too common for each to be treated as a national event. Guns have killed about 24,580 Americans since Newtown, according to Slate's estimate based on data from the Centers for Disease Control and Prevention.

Mass Shootings Since Newtown

Sept. 16, 2013 - Washington, D.C. - 13 dead (including gunman)

• Defense contract employee and former Navy reservist Aaron Alexis, 34, allegedly opened fire shortly after 8 a.m. inside building 197 in the Washington Navy Yard, killing 12 people and wounding more than a dozen others. Alexis was slain in a gun battle with police.

Sept. 11, 2013 - Crab Orchard, Tenn. - 4 dead

• Jacob Allen Bennett, 26, was arrested in the shooting deaths of a woman and three teenagers. Their bodies were found in a car about 50 miles west of Knoxville, Tenn.

August 14, 2013 - Oklahoma City, Okla. - 4 dead

• Daniel Livingston Green, 40, was arrested on four counts of first-degree murder, after his mother, sister and her two children were discovered fatally shot inside their home.

Aug. 7, 2013 - Dallas - 4 dead

• Erbie Lee Bowser, 44, a former teacher and Dallas Mavericks hip-hop dancer, was charged with two counts of capital murder after police said he attacked the homes of his estranged wife and his girlfriend, killing both women and two of their children. Four additional people were wounded in the attacks.

July 26, 2013 - Hialeah, Fla. - 7 dead (including gunman)

• Police say Pedro Vargas, 42, went on a shooting spree in his South Florida apartment complex, killing the building's two managers, a family of three, and a man returning from his son's boxing practice. Before the attack, Vargas called the police asking the dispatcher to run the license plate of a vehicle parked outside the building, after reporting he had been followed and threatened by people doing witchcraft. Vargas was killed by a SWAT team after an eight-hour stand-off with police, during which he took two people hostage. The hostages were rescued when the SWAT team stormed the apartment.

July 26, 2013 - Clarksburg, W. Va. - 4 dead

• Sidney Muller, 27, was arrested on four counts of first-degree murder for allegedly killing two individuals after a drug deal gone wrong. Muller allegedly then turned his weapon on two passersby, a father and his son who were delivering the local newspaper, killing them.

June 7, 2013 - Santa Monica, Calif. - 5 dead (including gunman)

• Police say John Zawahri, 23, armed with a homemade assault rifle and high-capacity magazines, killed his brother and father at their home and then headed to Santa Monica College, where he carjacked a woman, ordering her to drive him around while he fired at other people. The woman escaped unharmed but two other people were gunned down.Zawahri was confronted by police outside the school's library. They traded fire and police officers ultimately shot him dead.

May 11, 2013 - Waynesville, Ind. - 4 dead

• Four bodies were discovered in a home after a vicious killing that authorities said was a drug-related crime. One victim's son returned home to find the bodies and reported them to 911. Police say Samuel Sallee, 55, is the prime suspect in the case.

May 10, 2013 - Fernley, Nev. - 5 dead

• Jeremiah Bean, 25, was arrested days after allegedly killing an elderly couple in their home, then a newspaper delivery man and another couple nearby. Police say the first attack went undetected, giving Bean the opportunity to commit the three others. He was arraigned on 19 counts, including first-degree murder, arson and burglary.

April 24, 2013 - Manchester, Ill. - 5 dead

• Rick Odell Smith, 43, allegedly stormed a home, killing five members of the same family. Smith had been in a dispute with at least one of the victims, potentially over the custody of a child, police said. The five victims included a grandmother, her granddaughter, the granddaughter's boyfriend and their two children.

April 21, 2013 - Federal Way, Wash. - 4 dead (including gunman)

• A domestic-violence homicide claimed three additional lives before the gunman was killed by responding officers. Police say Dennis Clark III, 27, shot and killed his girlfriend in their shared apartment before killing two witnesses in the building's parking lot and a third victim in another apartment.

April 18, 2013 - Akron, Ohio - 4 dead

• Derrick Brantley and Deshanon Haywood, both 21, were each charged for the murder of four adults, two men and two women, who had been found shot in the head in a townhouse basement. Police say two guns were used.

March 13, 2013 - Herkimer County, N.Y. - 4 dead

• In a shooting rampage that spanned two upstate New York villages, Kurt Meyers, 64, allegedly took the lives of four people. Police say Meyers first opened fire in a barber shop in Mohawk, killing two customers, one a retired corrections officer. The gunman then fled to an auto care business in neighboring Herkimer and fatally shot an employee and a customer who was a 23-year veteran of the state Department of Corrections. According to authorities, the gunman had no money, no job and was maxed out on his credit cards.

Jan. 19, 2013 - Albuquerque, N.M. - 5 dead

• Nehemiah Griego, 15, is accused of killing both his parents and three younger siblings. According to police documents, Griego shot his mother while she slept, then killed his brother and sisters after they woke up. Griego told authorities he ambushed his father, who was returning home from work, with a semi-automatic rifle that his parents owned. All victims appeared to have gunshot wounds to the head. New Mexico authorities also report that the teen had planned to go to Walmart and randomly shoot people.

Jan. 7, 2013 - Tulsa, Okla. - 4 dead

• Brothers Cedric Poore, 39, and James Poore, 32, are accused of killing four women, two of whom were twins. The victims, found in an apartment, were all mothers, and a 3-year-old boy was also found unharmed.

Emily Thomas contributed reporting.

CORRECTION: We previously listed the Nikko Jenkins murders in Omaha, Neb., as a mass shooting. Because the killings took place over a 10-day period they have been removed from this tally.

This story appears in Issue 71 of our weekly iPad magazine, Huffington, available Friday, Oct. 18 in the iTunes App store.