On Friday, when Philadelphia begins mailing out the results of the citywide reassessment, much of the speculation surrounding Mayor Nutter's property-tax reform will give way to hard analysis of actual numbers.

Nutter is planning a morning news conference to discuss the Actual Value Initiative (AVI), after which most new assessments are to be posted to the Office of Property Assessment's website. All of the data should be available by early next week.

Owners should be able to use the website to learn what the city estimates their homes and other properties are worth, and begin to see how their 2014 tax bills will change.

The question for many taxpayers, especially if they think their assessments are wrong, then will become: How did the city determine my property's value?

In an interview this week, Chief Assessor Richie McKeithen explained the more-than-two-year process to tag actual market value to all 579,000 parcels in the city, acknowledging that there is an inescapable margin of error in such a mass appraisal.

"What we're trying to do is get closer to your market value," he said. "It's not a perfect system. There will be some things we'll have to clean up."

The Office of Property Assessment (OPA) has begun a new "first-level review process," in which property owners can talk directly to their assessors and argue for a change rather than seeking a formal appeal before the Board of Revision of Taxes.

Paperwork to seek a review with OPA will be included in the reassessment mailing and must be returned by March 31. Appeals to the BRT must be made by Oct. 7.

McKeithen, who has been attending community meetings around the city, said he wanted more communication with the public about assessments, which now will be updated annually.

"It's a process that doesn't have to be confrontational," he said. "We're just trying to get to the right value."

McKeithen cautioned that arguments over small changes in value are not likely to be successful. A variation in a house worth $300,000 instead of $310,000 would make minimal difference on a tax bill and would be difficult to quantify.

Single-family homes are primarily evaluated by looking at sales of comparable properties, and then examining the square footage, location, and condition of the property.

Assessors began by breaking homes into categories - rowhouses, condos, twins, ranchers. OPA then pulled data on 80,000 sales going back five years, showing what price every type of property had been fetching.

The city also was broken into 640 Geographic Market Areas - an attempt to group blocks where homes are similar and sell for similar amounts.

"The emphasis is to get the ultimate comparability," McKeithen said.

Assessors pulled five years of permits from the Department of Licenses and Inspections, to show whether homes had additions or other upgrades that might change values.

Then the assessors hit the street, walking every block in the city. They gave every home a condition code, from 1 to 7, from new construction to shell.

The assessors looked for variations like new windows or deferred maintenance. Does the roof need replacing? Have the bricks been repointed? Does the house have a garage?

Assessors also interviewed some homeowners, sent out questionnaires, and left door-hangers seeking more information on the interior condition of some homes.

OPA, with consultants' help, also did a land valuation study, trying to measure how much a square foot of land is worth in given parts of the city.

"This is the purest sense of the real estate theory," McKeithen said. "Location drives things first, and then it gets down to the characteristic of the particular property."

The Geographic Market Areas also can be adjusted through these methods, as neighborhoods change.

"Sales that used to be only $40 a square foot over here are now getting the same $60 as they're getting over there," McKeithen said. "That's an indication that that neighborhood is starting to push out."

That doesn't necessarily mean a new development is instantly going to affect a neighborhood of more modest homes. The value of the more modest homes would change only if people started buying them for more than they previously were worth.

For commercial properties, OPA asked owners to turn over information such as how much rent they collect or, for hotels, room and occupancy rates. That helps determine the worth of properties.

"If you're looking at something like the Marriott or Hilton, you're only going to have two in your particular location," McKeithen said. "They don't sell that often. Even when they do, the sale is so convoluted."

Before McKeithen arrived in 2010 from Washington, where he led a similar reassessment effort, only 3 percent of Philadelphia homeowners received bills based on their real estate's true value.

The rest, according to a 2008 Inquirer study, paid wildly disparate amounts based on assessments that were off the mark by an average of 39 percent.

Mike Mignogna, president of the Philadelphia Metropolitan Chapter of the Appraisal Institute, said OPA's approach was "the only way to do 570,000 properties in any reasonable amount of time."

"The only thing is, condition isn't readily apparent from the outside," he said. "If you're not going into the properties, you don't really know what's in the comparables or the properties you're assessing."

Ultimately, AVI's effect on various neighborhoods, including any unintended consequences, remains to be teased from the data in the coming weeks.

What Council and Nutter choose to do to alleviate AVI's impact on homeowners - longtime residents of growing neighborhoods, for example - also remains to be seen.

And, of course, the tax rate applied to those new assessments is not set. Currently, the administration says the rate would have to be between 1.20 and 1.25 percent - or between $1,200 and $1,250 per $100,000 in value.

If Nutter and Council approve tax breaks for homeowners, the rate must rise.

But, starting Friday, taxpayers and politicians finally can begin to judge how well McKeithen and his army of assessors have done their jobs. "I've done this in several places," McKeithen said. "I know it can be done here."