As cities grow and develop, their skylines can shapeshift dramatically. New towers rise, historic structures disappear, and once-iconic buildings fade back into a crowded forest of new construction. In a new paper published in the journal Landscape and Urban Planning, a team of researchers based in Turkey has developed a technique for tracking these changes using geographic information systems, or GIS.
With the historic skyline of Istanbul as their subject, the researchers made a 3D model of the city's skyline. With it, they were able to track changes to the skyline over the previous decade and to simulate the construction of hypothetical new buildings to understand their impact on the skyline.
It's a new approach to using GIS in combination with 3D building information – and one especially relevant in Istanbul.
"Such a great variation of the skyline over the last decade has revealed the fact that the need for an analytical approach to preserve the identity of the mega city is essential," the researchers write.
Istanbul is a split city, situated on two continents, Asia and Europe. It's had a unique history, and the architecture of the city reflects its varied past, according to Caner Guney, lead author of the article.
"Istanbul is primarily known for its Byzantine and Ottoman architecture, and the buildings here reflect the various peoples, religions and empires that have ruled it over the years," Guney writes, via email. "In each era a new architectural layer formed; many of these monuments remain intact."
But they may not always. As development pressures increase in cities all over the world, there's a greater chance that iconic or even historic elements of a city's skyline will be overshadowed or overpowered by new development. Guney argues that unless there's a clear record of the skyline, it will be impossible to preserve.
"Skyline development is a matter for public consultation and collective judgment," writes Guney. "The use of 3D GIS to engage public discussion in skyline development needs to be clear from the outset."
As a historic preservation issue, though, skyline preservation isn't a typical battleground, says John Hildreth, director of the National Trust for Historic Preservation's Southern office in Charleston.
"Sure, track it," he says. "But I think the hard part is when you talk about 'we want to try to preserve the skyline.' That’s a pretty difficult topic to get your arms wrapped around."
But Hildreth says that, in principle, the idea of preserving a skyline is a natural desire for a lot of people.
"Skylines are treasured parts of the city. Everyone has their favorite view of Manhattan or San Francisco or even here in Charleston," he says.
There have been some efforts to preserve skylines, though they're typically smaller scale efforts. Hildreth points to Philadelphia, where "more or less a gentlemen's agreement" prevented any building from rising higher than the huge bronze sculpture of William Penn atop City Hall – an informal rule that went unbroken for nearly 90 years, until 1987. Building height restrictions like these are common in other cities, though not explicitly written to protect the skyline.
In 2008, the National Trust for Historic Preservation listed Chicago's Michigan Avenue streetwall in its annual list of the 11 Most Endangered Historic Places. Hildreth says this was a skyline protection issue, as a proposed development project would have impacted the view of the street's skyline from various points in the city, including Millennium Park and Grant Park. That project stalled due to the recession.
Hildreth says the idea of using GIS to track and model skylines could be a new approach for making more comprehensive preservation efforts.
"Everybody has a visual memory of the city that either they like the way it is now, or they remember it back when, so being able to track those changes could definitely help policymakers," Hildreth says. But, he argues, not every skyline can or should be saved. "Skylines are dynamic things," he says.
Guney says the GIS approach he and his co-authors used has relevance in any city interested in preserving or maintaining historic skyline elements. The authors note that 3D applications using GIS are only beginning to emerge. Guney argues that sharing 3D spatial content on the internet can help to get more information out about the details of city skylines and historic views, and improve the utility of this technique. By creating maps and models, cities and citizens and preservationists can have a better understanding of exactly what a city's skyline is – and what could be lost.