for Cross-Disciplinary Collaboration on City Models

The goal of this project is to assist in bringing about a culture where people interested in representing buildings, street-scapes and neighborhoods as they are, as they were, as they might be or might-have-been, can easily share and re-use their work with each-other and with historians of the future.

This problem has not already solved owing to the fact that there are a lot of moving parts to a city model, difficult interoperability issues including data formats and coordinate systems. The solutions to these problems are beyond the scope of independent city modeling activities of municipalities, campus administrations and architecture firms. Several years of working with municipalities and designers and archival systems have led us to simple solutions that fulfil the principles of the ISO Reference Model for Open Archival Systems.

We hope that organizations interested in platform-independent digital asset management will find it expedient to adopt these free templates and tools. As a side effect, we may enjoy easier sharing of city model assets between agencies and applications. Fragmentary city modeling activities may begin to merge together. In this more fertile ecosystem of resources will support re-use of knowledge in city-modeling applications that has not been practical before -- including historical research and mobile augmented reality apps.

City Model Stewardship

Before digging into the technical details of How to manage a city-wide collection of 3D models, it will be useful to have a picture of the sorts of people for whom this scheme has been designed, and the personal and institutional motivations that make this effort worthwhile.

A scene from the Boston city model.

Roles and Motivations for Owners, Users and Contributors

There are many individuals, communities and institutions that are interested in exploring and contributing to a city-wide 3D model that reflects current street-scapes; that remembers past and speculative future scenarios. Design firms, municipal and campus planning agencies already maintain 3D models of their territories and immediate context. But currently it is rare to see these resources actually shared or systematically combined or preserved as cultural resources for future reference. In the case of public agencies, the problem is not a lack of will, but difficulties inherent in the combination of diverse data-sets that may be well-organized individually, but lack the forethought to be easily combined together in a re-useable way.

Municipal and campus planning agencies have the mission and means to collect diverse 3D data -- including the current built scenario and information about development proposals. While planning agencies may not be as interested as others in representing neighborhoods of the past, a good city model architecture will make it simple for municipal and campus planning agencies to preserve information about the present -- which will become historical information as the city develops.

The goal of the citySchema project is to provide an open-source, interoperable city model architecture that addresses the needs of the municipal and campus planning agencies and designers, that saves municipalities the cost of designing their own city model architecture, and provides a framework for integrating these models together, for long-term archiving, and for re-use of a metropolitan-scale city model in virtual and augmented reality systems.

Municipal or Campus Planning Agency

The citySchema architecture was designed to meet the needs of the municipal GIS departments of the City of Cambridge, Massachusetts and the Boston Planning and Development Agency (BPDA). The BPDA's mission statement:

In partnership with communities, the BPDA plans Boston’s future while respecting its past. By guiding physical, social, and economic change in Boston’s neighborhoods, the BPDA seeks to shape a more prosperous, resilient and vibrant city for all.

Among the agency's responsibilities is to guide the public review of large development proposals and to lead the planning and development of for designated special planning areas. This work involves much collection and two-way sharing of models for the purposes of visualization and as context for editable design models. In the future, 3D models will be part of the public record for development proposals, along with the digital two-dimensional models that are now included with proposals.

The BPDA Urban Design group has been maintaining a city-wide 3D model since around 2003. In 2014 the GIS department and pbcGIS began a project to develop a more detailed city-wide model that includes the building models developed by the UrbanDesign Technology Group. The GIS-based model enables web-based visualizations of the city model -- including projects that are approved but not yet built. In-house applications,such as ArcGIS Urban make it possible for planners and reviewers to investigate scenarios that are not yet part of the public review process.

Roles: Agency's Technical Curator

Fig Right

The agency's 3D model curator develops the 3D model from GIS data and digital 3D models that originate in design software. This role creates and re-uses programs that integrate 3D models with information resources including assessing information and content management systems associated with design review. The technical curator translates the GIS-based model into 3D models compatible with a variety of design-oriented 3D modeling tools and application development tool-chains. This role requires experience with 3D modeling and the issues that come up when working with 3D models in various formats. The technical user also has an understanding of GIS, relational database fundamentals and basic programming using ArcGIS Model Builder. Programming with python and javascript is useful, as well. The technical curator may be a full time staff member or a specialized contractor.

The Agency's Information Technology Manager

The IT Manager is accountable for taking care of the agency's information assets. This role involves hiring and evaluating the work of technical curator who may be employees or contractors. For the IT manager, a successful 3D model architecture results in a collection of assets that is sustainable without dependencies on particular individuals holding the position of technical curator. For the IT manager, it will be useful to understand the essential pieces of the city model, where they are stored, and the sorts of problems that are likely to occur -- including the possibility that the digital assets associated with the city model may need to be migrated from one software platform to another.

Standard-Based Archival Asset Management Approach

3D models of building shells or terrain tiles are digital documents reflecting observations and ideas, very similar to scanned photographs and drawings. In this sense, the architecture for developing, managing and sharing the city model has many of the functional characteristics of a digital asset management system for geographically and temporally referenced digital documents. When these 3D models become systematically referenced and retrievable, they can be very useful for generating a 3D context for understanding the interrelationships connecting other documents.

The citySchema architecture is based on the International Standards Organization Reference Model for Open Archival Information Systems.

Features and Benefits

  • Save time and money in developing a city model curation program from scratch.
  • Eliminate redundant effort. Participate in a resource-sharing and skill-building community.
  • Preserve historical and source information. Audit and recovery capabilities for all changes.
  • Protect against loss of knowledge when data management staff move to other projects or jobs.
  • Routine QC and validation of 3d models prevents unexpected roadblocks to exchange and migration.
  • Share and re-use city model assets in a variety of applications 3D modeling tools
    • Archival asset management systems
    • Virtual and Augmented reality
    • Open source tool-chains and viewers (e.g. Cesium, ThreeJS)
    • High performance proprietary enterprise GIS.
Model asset lifecycle involves GIS, 3D Model Authoring and Archival data structures.

As a bridge between the data-driven, expansive range of GIS, and the deeply hierarchal, but spatially limited world of 3D modeling tools, CitySchema substantially removes the difficulty of exchanging updates -- which can be published and subscribed between independent overlapping city models maintained at architecture firms, campus or municipal agencies, or developers of virtual and augmented reality applications.

Communication between GIS and fully-functioning 3D modeling tools provides non-proprietary pathways for validation, quality control, and migration for an institution's collection of information assets.

Streetscapes are part of our Shared Cultural Heritage

The world-wide web has brought about many new possibilities to access and connect information resources about people, places, things and ideas. Georeferencing is a powerful way of connecting resources that relate to places. HistoryPIN, Digital Commonwealth and AtlasScope are three examples of cultural preservation projects that use georeferencing to connect historical documents. These are part of a greater movement known as Digital Humanities, in that is bringing about new ways of discovering,connecting and presenting ideas.

Models of buildings and bridges may represent observations made at different times and at different levels of detail. Each model is worth preserving as a historical document with metadata describing its provenance.

Models produced for design review are also historical artifacts. Including models of ideas that were never built.

As the model is updated to reflect new conditions, we have a means of preserving and retrieving observations of the past condition. The same schema is also useful for developing and sharing models intended to illustrate historical conditions compiled from multiple sources.

3D models of terrain and buildings are not much different from georeferenced photographs, drawings and maps. It is only a matter of time before tools like the ones referenced above make use of 3D models as part of our cultural memory -- as observations that can be remembered and also as 3D base maps for contextualizing and connecting old photographs and other resources. It is phenomenal how much new information emerges when observations from different points of view and points in time are connected together.

How? CitySchema is an Mode of Exchange and a Collection of Tools

The first product of the CitySchema project is our catalog repository for the City of Boston Planning and Development Agency. It is ready to use now by the design and development community. Ready to be harvested by cultural preservation institutions. A working demonstration of the repository schema is published on GitHub to be forked and modified and by other agencies to organize and share their city model resources.

As the project moves forward in the second half of 2021, we wil be publishing the tools that develop and manage the model collections and their catalog. Currently these tools are based on Python, ArcGIS Pro (tasks and geoprocessing tools), Javascript and HTML.

As time moves on, we hope to engage with other interested parties to develop and share tools and workflows for using the metropolitan-scale city models with open-source workflows, including ThreeJS, Blender and Cesium.


This project began at the Harvard Graduate School of Design around 1998 with data from the Massachusetts Geographic Information System. Over the years it has received sponsorship, and collaborative support from the Harvard Center for Design Informatics, the Boston Redevelopment Authority, the City of Cambridge, Town of Brookline, The Open Geospatial Consortium, The Massachusetts Institute of Technology Facilities Department, Harvard University Planning and Real Estate, Sasaki and Associates, Architects and many others.

Extending the Boston Metro City Model

Currently, we are finishing several substantial improvements to the architecture for managing and sharing city models sponsored by the Boston Planning and Development Agency. This new architecture will allow us to connect several other projects that wil link several other projects across the Boston metro area.

  • Latest Metro3d Slideshow documents the effort sponsored by the BPDA.
  • Treatment of 3d Models as historical assets within a collaborative archiving and annotation tool like The Cambridge Digital Architectural Survey and History (another pbcGIS project!)
  • Linking of a vast collection of detailed historic maps being compiled by the Norman Leventhal Map Center at the Boston Public Library AtlasScope. We wil be tiling selected historical atlas maps for use in extending the Boston Metro 3D model back in time.

For more information, contact paulbcote at