SEE A MAN with a clipboard hanging outside your house? He could be from the city's Office of Property Assessment, which recently hit the streets as part of the effort to determine the market values of Philadelphia houses.

Chief Assessment Officer Richie McKeithen said that after a year of reviewing data and training staff, the office is heading into the field to examine the city's 423,000 single-family homes.

"It's a standard that you do inspections every year," said McKeithen, who came from Washington, D.C., about a year ago to set up the Office of Property Assessment.

The office was created after voters last year approved a plan to abolish the Board of Revision of Taxes, which came under fire in the Philadelphia Inquirer for a history of political patronage and inaccurate assessments. The BRT board remains in place to hear appeals.

About 50 inspectors began several weeks ago with houses in Manayunk, Roxborough and East Mount Airy. They will be moving through other city neighborhoods between now and April, McKeithen said.

Some inspections will just take in a property's exterior, while in others inspectors will knock on your door and ask questions about the condition of the home.

McKeithen said that the inspectors will show city-issued identification and will not ask for any personal information, like your social-security number. The city has not systematically done field inspections like this. The reassessment process is part of moving to a system that uses market values as the basis for tax bills, rather than the current system, which is based on "fractional" assessments.

"We are going to value the property based on what it would sell for," McKeithen said.

McKeithen said that he still expects to be on track to send out new assessments by October 2012.

That mailing would include your new tax bill, reached using the assessed value of your property and a new tax rate, which has not been determined.

McKeithen, who is in the process of hiring another 50 inspectors, said commercial and industrial properties also will be inspected.