Final answer:
The UCR is based on the voluntary reporting of crime by law enforcement agencies to the FBI. It is an annual publication that contains comprehensive information from police reports.
Step-by-step explanation:
The UCR is based on the voluntary reporting of crime by law enforcement agencies to the FBI. The FBI gathers data from approximately 17,000 law enforcement agencies and publishes the Uniform Crime Reports (UCR) annually, which contains comprehensive information from police reports. However, it's important to note that the UCR only accounts for crimes that are reported to the police, and not all crimes are reported due to various reasons.