The data is retrieved from this database of completed graffiti cleanup locations, which is maintained by the Mayor's Community Assistance Unit (CAU).

This database is updated as graffiti cleaning crews complete their work, and EveryBlock retrieves the data on a nightly basis.

Note that cleanup dates listed here are approximate and represent the date that the cleanup was entered into the database, which may not be the day the graffiti was actually removed. This is because of the way cleanups are reported. Cleanup crews are dispatched to clean a number of locations over the course of a few days. These groupings are organized geographically by Community Board into sets of locations that have completed waivers. The cleanups are reported as complete once the entire set is finished. This accounts for the "bunching" of dates in the data, with no cleanups for a number of days in a row and then hundreds listed in one day.

Graffiti comes to the attention of the city mainly through citizen reports and the efforts of the Police Department (PDF). The NYPD offers $500 rewards for the arrest and convictions of anyone who commits graffiti vandalism. Dial 911 for crimes in progress, and 311 to provide information about existing graffiti.

Much of the graffiti removal performed under this program is done on private property. According to city law (PDF), building owners are legally responsible for removing graffiti on their property, but building owners can have graffiti removed by the city at no cost by filing a waiver (PDF) with the CAU. This waiver allows crews to enter the property and to using high pressure technology, painting, chemical solvents on the graffiti. Once the waiver is returned to CAU, the graffiti will be removed within an average of four to six weeks.

See also the list of pending graffiti cleanups. Note that not all completed cleanup records have a corollary pending cleanup record. In these instances, the waiver was received and the cleanup was performed on the same day.

Go here for more information on the New York's Citywide Anti-Graffiti Initiative, including links to the efforts of the NYPD to prevent graffiti and frequently asked questions.

The CAU also offers The Mayor's Paint Program, which allows community and volunteer groups to plan and execute their own cleanup projects with supplies and paint provided by The Mayor’s Office. Paint program locations are not represented in the cleaned graffiti list.

Mayor's Community Assistance Unit Web site, the New York Police Department Web site, and Ray Carrero of the CAU.

Definitions:
Waiver date: The date that a waiver was received by the CAU from a building owner and entered into the system. A waiver is one-page document granting the city the right to enter the property and to remove graffiti. It releases the city from liability and also gives the owner the ability to indicate the best time of day for cleanup, and a preference on color of paint to be used.