Vacant housing data set not accurate says Baltimore Slumlord Watch blogger

Technically Baltimore reported last week on Elliott Plack’s map of vacant housing in Baltimore city, assembled with the help of Open Baltimore data. According to that data, there are 15,928 vacant buildings in the city.
But the Baltimore Slumlord Watch blogger, who goes solely by the name “Carol” and has been keeping tabs on vacant buildings in the city since 2009, says that number is too low to be accurate.
“I think that the map is beautifully done,” she says. “I just hesitate to let it stand as sort of this definitive number.”

Carol says the main problem with using Open Baltimore’s number is the inaccuracy of the data. She says there are many vacant houses Baltimore city doesn’t know about, a symptom of how the city defines what is, and what is not, a vacant property. Baltimore city defines a building as vacant if it is “an unoccupied structure that is unsafe or unfit for human habitation or other authorized use,” which is found in Section 115.4 of the Building and Fire Codes. Additionally, the city issues a vacant building notice for any such properties.
As the city’s Vacants to Value website notes, “Although a property may be unoccupied, it is not considered vacant until it meets this criteria and a violation notice has been issued.”
Other cities have similar problems — like, yes, Philadelphia — in defining what a vacancy is, so data is often fought over. Think about it: is a building vacant when utilities are shut off, or when mail stops getting delivered or the moment when no one calls it home? There is more gray area than you might think.
“[The] problem with using city data is there are thousands [of vacants] that the city doesn’t know about,” says Carol. “This is a big city. Of course they’re not going to know about all of them. You have the dilapidated run-down ones that the city doesn’t know about. Then you have ones that look perfectly normal outside.
“My personal feeling,” Carol says, “is whatever [number] the city has, you can double it.”