Property assessments in Philly vary great Credit: Aaron Kreider / via reddit

Updated Feb. 24

Since the beginning of April, many Philly residents have opened their mail to find an envelope full of sticker shock.

The city just rolled out new property assessments — officially called “Proposed Valuations for Tax Year 2019” — and while some home values decreased, many went significantly up. Per an Inquirer/Daily News analysis of the data, the median market value of single family homes in Philly jumped 10.5 percent year over year.

Since 2014, Philly’s Office of Property Assessment has been updating its valuations, trying to correct under-assessed properties to strengthen the city’s property tax base.

But deciding which plots to reassess and how much to boost (or decrease) their values is done at the OPA’s discretion — and the methodology, which can feel pretty random, often leaves homeowners confused.

“What strikes me is how arbitrary it seems,” wrote one Fairmount resident on reddit Monday morning. “The houses on my block are all in similar condition, but some (like mine) got hit much worse than others.”

“My next door neighbor has an identical plot size (both mid-block) and their land value is now 30% less than mine,” commented a different person in the same reddit thread. “It makes absolutely no sense.”

These discrepancies aren’t obvious when you look at the overall assessment data, but they come into sharp relief when the detailed info is plotted on an interactive map.

That’s exactly what Philly programmer and web developer Aaron Kreider has done.

Kreider, founder of progressive toolkit sites Campus Activism and Justice Map, took all the OPA data, calculated the percent change in assessed value per square foot of living area, and mapped the shift for every single property for which it was available.

The resulting map allows you to scroll around and view the changes at a granular level, checking parcel-by-parcel how much the values changed.

Click for interactive map Credit: Aaron Kreider

Zoomed all the way out, you can view general neighborhood trends, like the big increases in Fishtown or decreases in Fairhill. But zoom in and disparities quickly appear, with dozens of blocks showing tracts in deep blue (value up more than 20 percent) right next to those in deep red (down 15 percent or more).

Update: There’s now a second map, with additional filtering tools.

Inspired by Kreider, Philly coder Aaron Bauman created a clickable version of the visualization. On Bauman’s version, you can move sliders to refine what the map displays. For example, as Bauman tweeted, “Want to see only the properties whose assessments went up MORE than 20%? All 120,000 of them?” This is the place to do it.

Many factors contribute to each property’s final value, including age of structure, its condition, its use and, for homes, recent sales of similar properties nearby. Which is to say, these maps could come in handy if you’re scratching your head about the number on your new assessment.

Homeowners can ask the city to reexamine their “proposed value” by requesting an OPA review by May 25.

Danya Henninger is director and editor of Billy Penn at WHYY, where she oversees the team, all editorial decisions, and all revenue generation — including the membership program. She is a former food...