An abandoned home is seen with the Detroit skyline in the background on September 5, 2013 in Detroit, Michigan. (Photo by Andrew Burton/Getty Images)

The next time you're tempted to gawk at Detroit ruin porn, appraising scenes of decayed architecture and apocalyptic lots as if they were fine art, stop and consider these numbers: It will likely cost the bankrupt city a staggering $850 million to raze and clean up the tens of thousands of long-abandoned single-family homes all over town. It will cost another $500 million to $1 billion to do something about the large-scale commercial and industrial property rot.

That's vastly more than the city has allotted for the task (about $450 million). And it's money that Detroit can't spend directly on services -- parks, firefighters, pothole repairs -- for the people who have stuck around.

These numbers come from a report released this week by the Detroit Blight Removal Task Force on the results of a  manual survey of 377,602 property parcels in the city. Nearly one in three structures in Detroit needs some kind of intervention, according to the analysis. That covers 78,506 structures that the report has deemed "blighted" or showing indicators of blight, as well as 6,135 lots that have effectively become neglected dumping grounds.

This is probably one of the cruelest realities of a shrinking city: It costs a tremendous amount of money merely to demolish and recycle what other people have left behind. And many of those costs must inevitably be borne by the neighbors who remain. Detroit is facing this reality on a scale that's never been seen before in an American city. More than 1.8 million people lived in the city in 1950. Now that number is closer to 700,000. That effectively means Detroit once had more than twice the housing it now needs.

"We need to recognize the volume of blighted structures did not happen overnight," the report declares. "Detroit’s conditions are the physical result of dire economic and social forces that pulled the city apart over many decades."

The empty lots, vacant homes and shuttered industrial plants that attest to this exodus are not evenly spread across the city. And so Detroit -- as New Orleans did after Hurricane Katrina -- will face difficult decisions about where to focus its efforts, prioritizing those places where investment will have the greatest impact on people who still live in the city. By Detroit's reckoning, no city has ever addressed more than 7,000 blighted structures in a year. The task force is proposing to eradicate all blight in the city in the next five years, lest blight beget more blight, with the problem continuing to spread beyond the city's ability to keep up.

To understand just what the city is up against, this map shows the 44,077 structures that have been recommended for removal that meet the task force's definition of blight:

Detroit Blight Removal Task Force

That definition includes properties that are exposed to the elements, not structurally sound, need major repairs, have suffered fire damage, or have been turned into neighborhood dumping grounds. This second map shows another 38,429 structures that have "blight indicators," because they were unoccupied at the time of the survey, or because the county, local land bank or Fannie Mae or Freddie Mac had taken ownership:

Add them together, and you get this:

Detroit Blight Removal Task Force

Tens of thousands of properties in the city have gone through tax foreclosure because the owners went more than three years without paying property taxes. And tens of thousands more are poised to enter that process, making the city of Detroit, in the report's language "a very large and inadvertent landlord." Another 118,000 "tax distressed" properties are on their way to entering this tax foreclosure cycle, representing more than $500 million in overdue property taxes and penalties.

This means that every blighted property infects the city multiple times: first by robbing it of property tax revenue, then by saddling it with the costs of demolition if no one wants to buy it at auction. That diagnosis doesn't even touch on the consequences for neighborhoods, as abandoned parcels drag down property values and discourage new families from moving in.

The report identifies "tipping point" geographies suspended in between the most stable and the most abandoned neighborhoods where the task force recommends focusing resources first. Intervene in these places immediately, the report suggests, and they have the highest potential to stabilize and attract new investment.

As for the alternative? "Lack of intervention has the potential to quickly result in significant decline in stability, occupancy, and overall population," the report says. "Shortly thereafter, disinvestment, increases in vacancy, blighted properties, and crime is likely to follow."