City Schema

A Schema for Cross-Disciplinary Collaboration on City Models

Why? Expensive observations and effort are going to waste.

We know that in the Boston area there are several municipal governments, campus administrations and architecture firms that maintain broad-scale 3D models for their territorial interests and surrounding area. These models are used primarily for visualizing proposed changes. Many of these models overlap with each-other resulting in redundancy of details and of effort. Opportunities to systematically remember the past form of the city is fragmented and impractical to collect -- even though millions of dollars are spent annually by different agencies to collect systematic snapshots of the city.

Everyone agrees that ongoing information stewardship is a good idea, but this does not seem to be a pattern that emerges spontaneously!

We do not see region-wide collaboration in the development and stewardship of city models because figuring out how to organize the work is very time-consuming. Individual participants don't have the motivation or skills think through the needs of collaborators from different disciplines with tools and workflows that pose real difficulties for information exchange.

This project, funded by the City of Boston Planning and Development Agency Office of Digital Cartography and GIS is designed to diminish these obstacles by working with contributors from the spectrum of disciplines to create a ready-made framework that is designed to preserve information about the shape of places in the city through all of the hand-offs that are required.

What? Schema for Annotating, Preserving and Sharing Detailed City model Assets

This project takes an archival asset-management approach organizing city models. In this sense, 3D models of building shells or terrain tiles are digital documents reflecting observations and ideas, very similar to scanned photographs and drawings -- just a different format with a different previewer plug-in. When these 3D models become sytematically referenced and retrievable, they can be very useful for generating a 3D context for understanding the interrelationships connecting other documents.

Most of the 3D models in the Boston 3D collection originated with a city-wide photogrammetric survey from 2011 (InfoTech) which yielded a crisp terrain mesh, planimetric ground plan and detailed building footprints with heights. In 2012, the same photorammetry was used to generate more detailed 3D models of buildings for about one-fifth of the buildings in the city of Boston (CyberCity3D). Large projects that have passed through the BPDA's project review process have been meticulously crafted by the BPDA's in the sorts of 3D modeling tools CitySchema provides a means of recording the provenance of models while the information is ready-to-hand. Each model is traced back to its original source format.

As the model collection is developed, models change their status from Proposed to Active and eventually Historic, and these changes are properly time-stamped. Models of historic conditions continue to be managed and retrievable. CitySchema also provides a means of alternate models of the same bridge or building any one of which could be used as the default.

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.

The City Schema Repository is a self contained snapshot all of the city model components in a directory structure and catalog files that make make each 3D model systematically addressable. This catalog is put to use to render a clickable tile map for accessing tiled resources, and for each tile, a collection of building models with the tile-specific catalog and clickable index map that demonstrates the addressing of individual building models along with the attribute information for each model.

The catalog repository is a complete, self-contained exchange package as described by the International Standards Organization Reference Model for Open Archival Systems. It is completely functional without a connection to the internet. If the Catalog Repository is placed on a web server, it instantly provides http endpoints for Models and their metadata to that can be referenced by the burgeoning world of linked data and digital humanities applications. We hope to extend it soon to accommodate interfaces for subscription to model updates as described by the Open Archive Initiative Protocol for Metadata Harvesting.

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.

Who? Acknolwedgements

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.

For more information, contact paulbcote at