Inspired by lessons from New York City’s 9/11 recovery, the MUDDI standard developed through OGC collaboration is helping cities better map and manage underground infrastructure.
When the World Trade Center collapsed on September 11, 2001, the devastation above ground was visible to all, but an equally perilous crisis was unfolding beneath the surface. Fires raged deep underground, threatening critical utilities and transportation tunnels, and making it dangerous for firefighters and recovery crews to even approach. Hidden below the debris lay a 200,000-pound tank of liquified freon, part of the towers’ air conditioning system. If the heat reached it, the gas could have exploded or released deadly phosgene fumes. Yet no one had a complete, accurate picture of what lay beneath the site. Each agency and utility held fragments of incompatible data, and it took more than ten days to piece together a coherent underground map of the damaged infrastructure. When the freon tank was finally located, firefighters were able to douse the surrounding area, averting another catastrophe in a city already in crisis.
The experience also exposed a fundamental challenge that cities around the world continue to face: fragmented and incomplete information about the infrastructure hidden beneath their streets.
That harrowing crisis revealed a truth that still resonates: cities cannot plan, build, or recover effectively if they lack a clear understanding of their subsurface environment. For urban planners, the networks of pipes, cables, tunnels, and geological layers hidden below ground are as vital to resilience and sustainability as the infrastructure visible above it.
From crisis to collaboration
In the mid-1990s, New York City began developing a photogrammetric basemap that would serve as the foundation for all municipal geospatial data. The Department of Environmental Protection and other agencies used it to build compatible layers for water, sewer, and surface infrastructure. When 9/11 occurred, the city had a partially functioning enterprise GIS, but much of its underground infrastructure was still unmapped.
In the years that followed, planners, engineers, and geospatial experts worked intensively to close the data gaps that had hindered the city’s emergency response and complicated construction, excavation, and maintenance. While the city’s enterprise GIS expanded to include more than 1,000 layers, progress on underground utilities lagged. Private utilities digitized their networks independently, without adopting the city’s basemap or shared standards. When Hurricane Sandy hit in 2012, storm surges flooded coastal areas and caused tens of billions of dollars in damage—some of which might have been mitigated with better underground data and coordination.
Building the framework: MUDDI
More than two decades later, the lessons from New York have helped shape a new generation of geospatial data standards being applied worldwide, from U.S. cities to national initiatives including the American Society of Civil Engineers (ASCE) standards for underground infrastructure (ASCE 38 and 75); the European INSPIRE data models which serve as the basis for underground utility mapping systems in Flanders, Denmark, Scotland, and the Netherlands; and the development by the Open Geospatial Consortium (OGC) of the Model for Underground Data Definition and Integration (MUDDI), which serves as the basis for the United Kingdom’s recently initiated National Underground Asset Register (NUAR).
Conceived by experts from New York City and the U.S., the U.K., Singapore, Belgium, Canada, and Denmark, MUDDI builds on best practices from established and proven geospatial utility data models, including ASCE 38 (Subsurface Utility Engineering – SUE), ASCE 75 (As-Built), the European Commission’s INSPIRE Utility and Government Services data specification, as well as the Network Utility Application Domain Extension for OGC’s CityGML standard. Together, these provide a foundation for accurate 3D underground mapping, enabling the geometry, attributes, and relationships between subsurface elements to be integrated across utility networks.
The goal of MUDDI is to create a common language and structure for underground data—making it possible to align utilities, geology, and surface infrastructure across jurisdictions. Over time, it has evolved into an overarching framework capable of improving compatibility among national and regional models and supporting a wide variety of use cases, from construction coordination to emergency management.
New York City’s next chapter
Even after 9/11 and Hurricane Sandy, New York City hesitated to launch a city-wide integration program. Concerns over data security, costs, liability, and loss of control slowed collaboration between private utilities and city agencies. But global progress, including the launch of the UK’s NUAR, helped demonstrate what was possible.
In November 2025, New York City announced the 3D Underground (3DU) initiative—a $10 million program funded through U.S. Department of Housing and Urban Development disaster recovery grants—to develop a secure, shared 3D model of the city’s underground utilities and geology. The project brings together city agencies, utilities, and the State Public Service Commission, with Columbia University digitizing more than 20,000 boring records to model the city’s geology, recognizing that underground utilities and geology are deeply intertwined.
This marks a significant shift for the city, moving from fragmented utility datasets toward a shared, interoperable framework inspired by global best practices.
Why underground data matters for planning
For planners, MUDDI opens new ways to manage the “city beneath the city.” Traditionally, each utility or public agency maintained its own underground records, often incomplete, outdated, and incompatible. This lack of coordination led to costly excavation strikes, construction delays, and dangerous uncertainty in emergencies.
By providing a shared framework, MUDDI allows underground data to be assembled and visualized in 2D as well as 3D across systems. For planners, this means they can:
- Coordinate development by understanding where existing infrastructure lies and where capacity exists for growth.
- Improve capital project design by identifying potential utility conflicts before construction begins.
- Reduce accidental utility strikes, especially those involving fuel or electric transmission lines that can cause fires or explosions.
- Support disaster planning and response by ensuring emergency managers have rapid access to accurate, consolidated underground data.
- Link with digital twins and Building Information Modelling (BIM) to create an integrated view of the built and natural environment.
For example, a city planning a new transit line or rezoning a densely built-up corridor can use MUDDI-based data to assess the entire subsurface before breaking ground—preventing a multimillion-dollar construction project from being halted by an unmapped fiber-optic cable.
More comprehensive digital maps also enable AI-powered analysis to identify maintenance needs and optimize construction coordination. Members of the OGC MUDDI Standards Working Group estimate that improved underground data could reduce capital and maintenance expenditures by at least five percent—saving billions across U.S. cities.
The MUDDI Environmental Subcommittee is exploring how surface flooding interacts with underground systems. By mapping how stormwater enters and damages basements, tunnels, and utility pipes and conduits, planners can better anticipate risks and design more resilient infrastructure—whether in New York, or in flood-prone regions like Asheville, North Carolina, and Kerr County, Texas.
New York and beyond
While the U.S. does not yet have a comprehensive underground utility mapping plan, the UK’s NUAR offers an important global case study. Led by the Department for Science, Innovation and Technology, and operated as a service for public and private sector users by Ordnance Survey (Great Britain), NUAR applies MUDDI’s principles at national scale, aggregating data from hundreds of Underground Asset Owners to create a secure, standardized digital map of the UK’s buried infrastructure. The UK estimates that NUAR will save $4.5 billion over a decade through reduced utility strikes and improved coordination, while also providing instant access to data and reducing the number of organizations that must be contacted for utility locates. NUAR is speeding up the average time it takes to get hold of Underground Asset records from six days to six seconds. It shows how standards like MUDDI can move from concept to operation, translating interoperability and transparency into measurable public value.
One standard, many benefits
MUDDI’s strength lies in its flexibility and in its ambition to harmonize underground data models into a family of compatible standards. It does not replace local or national systems—it connects them. A city like New York can build a detailed map of utilities within its borders, while a program like NUAR can operate at a national scale, with both able to exchange their required data seamlessly.
As compatible layers are built across jurisdictions, U.S. regions will eventually be able to link underground networks across shared city and state boundaries. The process may take time, but we’ll get there one city, one county, one state, and one tribal nation at a time.
The way forward
For urban planners, the ground beneath our feet represents both a challenge and an opportunity. Managing it well requires seeing the city in full, above and below the surface. The MUDDI model, and projects like NUAR that build on it, demonstrate the value of shared data standards in creating safer, more resilient, and more sustainable cities.
As underground mapping expands across the U.S., a broader vision comes into view. The same standards that connect pipes and cables below ground can also link to features above it—streets, trees, traffic systems, and buildings—offering planners a unified picture of how the built and natural environments interact. This integration, supported by advances in AI and digital twins, is opening new frontiers in planning analysis and decision-making.
As populations grow and infrastructure ages, cities that can understand and manage their underground assets will be better equipped to plan confidently for the future. MUDDI’s vision, born from the lessons of 9/11 and carried forward through global collaboration, shows that even the parts of a city we cannot see can be planned, managed, and protected.
About the authors
Alan Leidner is a geospatial consultant, NYC GISMO President Emeritus, and OGC Liaison. He holds an MS in Urban Planning from Pratt Institute and worked for the NYC Department of City Planning for ten years. He led New York City’s emergency mapping efforts following 9/11 and currently serves on the U.S. National Geospatial Advisory Committee.
Carsten Rönsdorf is the Product Manager for the National Underground Asset Register at Ordnance Survey, where he has led international collaborations on underground data management and serves as co-chair of OGC’s MUDDI Standards Working Group.
Acknowledgment
The authors acknowledge the contributions of the OGC MUDDI Standard Working Group and the editors of the MUDDI Standard (OGC 23-024) including: Alan Leidner (NYC GISMO), Wendy Dorf (NYC GISMO), Andrew Hughes (British Geological Survey), Carsten Rönsdorf (Ordnance Survey Great Britain), Neil Brammall (UK Government Digital Services), Phil Meis (UMS), Dan Colby (UMS), Liesbeth Rombouts (Flemish Information Agency), Dean Hintz (Safe Software), and Joshua Lieberman (Open Geospatial Consortium). The development of MUDDI was supported by an international network of experts from New York City, the United Kingdom, Singapore, Belgium, Canada, Denmark, and other participating nations. Special thanks to Mark Reichardt, former CEO of OGC, and George Percivall, former CTO of OGC, who were instrumental in initiating the MUDDI project. Also, thanks to Mary McCormick and the Fund for the City of New York for providing initial funding for the MUDDI initiative. Additionally, thanks to the American Society of Civil Engineers (ASCE) for the development of the SUE and As-Built standards.
For more information
See the OGC MUDDI Standard (Document 23-024):
https://docs.ogc.org/is/23-024/23-024.html
