A rookie Virginia police officer working her first official shift was shot and killed Saturday while responding to a domestic violence dispute, authorities say. The officer, Ashley Guindon, was killed a day after being sworn in to the Prince William County Police Department.

Guindon, 28, was the 22nd police officer killed in the United States this year, according to the Officer Down Memorial Page, which has among the most comprehensive and timely national statistics on the Web. It was the first such incident this year in Virginia.

Since 1791, according to the site, more than 22,000 police personnel — federal, state, local and tribal (and K-9) — have been killed in the line of duty. The country’s most populous states — California, Texas and New York — lead the nation in police killings. That’s no surprise given the size of their populations.

The map below, however, attempts to normalize the state totals by adjusting for the total number of police officers in each state as of 2011 — the latest data available from the FBI. (Police forces by state vary in size based on a number of factors, including density. The District of Columbia, for example, is among the least-populous “states” listed in the data, but it has the highest rate of officers per capita in the country. That’s because it experiences a huge influx of daily commuters from Virginia and Maryland each day — and because of the tourism and security that comes with being the nation’s capital).

By that crude measure, Kentucky has proportionally had the highest number of killings, with roughly 85 per 1,000 officers, followed by West Virginia (47) and Montana (42). Florida (11), Arizona (12) and New Hampshire (13) — states, incidentally, with older populations — have the lowest rates, respectively. Again, this rate isn’t perfect, but it’s better than viewing the raw totals (which looks like a population map).