Consequently, homes that are selling are skewed toward the upper end of the market, he said. "Young households and low-income households just aren't qualifying for mortgages right now."
In the very low-income neighborhoods "you've got very little sales activity," including parts of North and West Philadelphia, lower Northeast, Kensington and Frankford, Gillen said.
While in the city's outer ring, housing prices "have been sort of flat." These areas include the upper Northeast, upper Northwest including Mount Airy and Chestnut Hill, Roxborough, deep South Philadelphia, and Eastwick-Southwest Philadelphia.
In contrast, Northern Liberties, University City, Queen Village, Graduate Hospital, and Bella Vista have seen "significant price inflation."
Interviews with several Realtors backed that up.
In Fishtown, north of Girard Avenue, the housing market has "picked up, and people are getting more confidence," said Realtor John Szymanski, who has sold properties there for 35 years. "The difficulty right now is getting people approved for mortgages."
"We are getting people to buy properties, but lenders are harder than they've ever been in their criteria on approving buyers."
He cited a businesswoman with cash to put 20 percent down on a $150,000 home, and a credit score of 809 on a scale where 844 is the top.
"We have been waiting 3 1/2 months. It's ludicrous what they are making people go through to get mortgages."
In the lower Northeast neighborhoods of Oxford Circle, Castor Gardens, Mayfair, and Torresdale, the housing market has picked up 2 percent to 3 percent. With interest rates of 3 1/2 percent, there are "great deals for people who can buy," said Realtor Christopher Artur.
Realtor Julie Welker said sales, including in North Philadelphia, are "ticking upward." She pointed to multiple-listing research that citywide home sales were up 5 percent this year, compared with the same period in 2011. The median home sale price is also up - from $125,000 in 2011 to $131,000 so far in 2012, Welker said.
Not everyone is seeing that trend. "To be quite blunt, property values unfortunately are depreciating," said Realtor Jim Skowronski in the city's Richmond section.
"The amount of activity for people purchasing properties has slowed down. It's the economy," he said. "People are reluctant to pull the trigger to buy a property because they may not have a job two weeks from now."
"It's not like the sky is falling, but the activity is nowhere near where it was four years ago."
Gillen, the Fels economist, said homes within walking distance of transit stops "have held their value quite well," regardless of which neighborhood.
In the last decade, with energy costs so high, homes that are centrally located in "walkable" neighborhoods with access to public transit "have carried a real premium."
"That's in general why the city has outperformed the suburbs during this downturn" in housing values. "High energy costs have prevailed in this economy."
Contact staff writer Linda Loyd at 215-854-2831 or email@example.com.