New York's system, which has cost about $20 million to develop over the past decade, helped coordinate emergency responders on Sept. 11, 2001. And in the aftermath, the underlying map was combined with thermal data detected by low-flying planes to show where fires and dangerously hot steam lurked in the World Trade Center rubble.
Now, the GIS system is aiding security plans for this summer's Republican National Convention at Madison Square Garden.
Previously, such plans relied heavily on "paper maps that showed no more than a thin line representing a street," said Lawrence Knafo, deputy commissioner of the city's information-technology department.
While that helped determine which streets should be closed, or where to position police officers, the new system lets authorities do much more.
For example, GIS can measure streets and sidewalks to determine how many people will fit in a given space. Or building floor plans can be overlaid on the map, giving emergency agencies a wider perspective on how to plan for problems - and react to them if necessary.
"By assessing the location of something and then combining it with what's around it, you're able to make a decision you were never able to make before," said Erich Seamon, GIS manager for San Francisco, where City Hall uses mapping software to monitor resources and police tap it to track crimes by location.
In fact, GIS is so good at changing how things get done that some resistance is inevitable.
In a test on Staten Island, New York City officials used the system's knowledge of building sizes at each address to estimate the amount of garbage that certain streets ought to produce. The data helped plot the most efficient routes for trash pickup.
But officials in the technology department said they feared that expanding the mapping function to garbage pickup elsewhere in the city could rankle the sanitation workers' union.
Harry Nespoli, president of the union, said he was unaware of the GIS test, but expressed doubt that trash service could be improved by software.
"We are not computers, you know. We are human beings," he said. "Does a computer get lunch time? Does a computer sprain his ankle? Does a computer die like one of my members did the other day? We have very, very efficient managers on this job. They came up through the ranks. They know the best way to pick up the garbage."
Overall, however, not much about these systems is controversial. Their most sensitive data are walled off from the public on secure servers.
However, some morsels are plugged into public Web sites in New York and San Francisco, for example, that combine aerial images, zoning records and information about local schools, government representatives or cultural attractions.
New Zealand uses spatial software to make sure tectonic shifts are reflected in property records. In California's vineyard-rich Sonoma County, agricultural commissioners rely on GIS to decide whether to grant pesticide-spraying permits, because they can check within minutes what schools, homes and medical facilities lie near the fields in question.
"It's still an emerging technology, but it's come a long way in the last couple of years," said Paul Buzanski, Sonoma County's GIS manager. "It's almost endless what we can do with it."
