As COP31 unfolds in Antalya, Türkiye, over these two weeks, resilient cities and the built environment are taking a prominent place on the summit’s agenda. For the first time, a COP presidency has placed urban climate action on the leaders’ agenda, and Türkiye deserves credit for this. Cities consume most of the world’s energy and are also among the hardest hit by floods, extreme heat and earthquakes.
There is a target for urban programs: cut the energy intensity of the global building stock by at least 25% by 2035. I support it. Last week, Royal Institute of British Architects (RIBA) President Chris Williamson made the case that digital twins – a virtual replica of a physical building, asset, or system that uses live data to simulate behavior, monitor performance, and guide decisions across its lifecycle – can improve how information flows through a building’s whole life. I would add one condition: a twin is only as good as the survey beneath it.
After 13 years in municipal infrastructure, first in Istanbul and now near Chicago, one question keeps coming back to me. How will a city know it has reached the target 25% if it does not know what it has today? I believe resilience starts with a map, one that shows both what stands above the street and what runs beneath it.
Energy intensity is energy used per square meter. Utilities know the energy; the square meters are harder to find. Many cities have no reliable inventory of their buildings, and unpermitted additions never reach the files. Airborne LiDAR closes this gap. A laser scanner on an aircraft records the height of every roof and street, and from that point cloud we build a 3D model with a measured volume for each building.
Istanbul has done this at scale. From 2015 to 2016, I worked at BİMTAŞ, the Istanbul Metropolitan Municipality's engineering company, on the team building the city's 3D model. About 5,400 square kilometers were scanned from the air at 16 points per square meter. The result was Level of Detail 2 (LoD2) models of roughly 1.5 million buildings, with 3,800 landmarks such as mosques modeled in finer detail. Checked against zoning plans, the same data could flag floors and additions that never received a permit.
The same model shows which roofs suit solar panels and which neighborhoods need insulation most. When the target's wording moved from "efficiency" to “intensity” this summer, critics warned that intensity can fall without real upgrades. A city with a measured building stock can track both.
The other half of resilience is underground, and Istanbul was reminded of it a month ago. On Oct. 14, parts of the city received more than 240 millimeters of rain in a single day, one of the highest readings since 1985. The Kağıthane stream overflowed, and floodwater carried cars through the streets of Ayazağa. At least six people died in Istanbul, and the governor said about 3,000 homes and workplaces were badly damaged.
Rain like that would overwhelm any city. How much harm follows depends on what lies under the street: sewers, storm drains, stream channels and whether anyone knows exactly where they run and how much they can carry. Chicago learned this decades ago. Its combined sewers used to push untreated water into the river and Lake Michigan during heavy rain. The region answered with the Deep Tunnel: more than 170 kilometers (105 miles) of rock tunnels feeding large reservoirs, under construction since the 1970s.
Projects like this depend on knowing exactly what is already in the ground, and that knowledge is often missing. In my daily work at a suburban public works department, much of the time goes into confirming what the records say: the depth of a manhole, the size of a pipe, whether a line on a 1960s plan still exists. Many municipalities, in the United States and in Türkiye alike, keep this information on paper or in the memory of senior staff. When those people retire, it leaves with them.
The two halves belong in one model. LiDAR – a remote sensing technology that uses laser pulses to measure ground elevations – supplies the elevation data every drainage study needs, while a GIS asset inventory – a digital mapping system that records infrastructure data – captures each pipe’s size, age and condition. Together, they show where water will collect, which streets will flood first and which repair will protect the most homes per dollar. They also make projects bankable.
Türkiye has set up a mechanism through ILBANK, its development bank for municipalities, to help cities in developing countries turn resilience plans into fundable projects. In my experience, such plans stall at the quantity takeoff and the cost estimate long before they reach a lender. Both depend on data.
So my proposal is modest. Alongside the 25% target, the Antalya Compact should ask participating countries to build a basic digital inventory of their cities: a 3D building model plus a GIS map of the networks beneath, updated every few years. Lenders, ILBANK's new mechanism among them, could fund it as a first-step project. It costs little next to the construction it will guide.
U.N. climate chief Simon Stiell has called for an “era of implementation.” Targets are written in percentages but delivered street by street, and implementation starts with knowing what you have. A city that can measure itself can plan, borrow and build with confidence. If COP31 wants to be remembered for implementation, a good map is a practical place to start.
