Hyper-Layering Architecture and a Minimal Map Model

Exploring Questions within the Maps for HTML Community Group

Over the past year, we have been revisiting the Hyper-Layering Architecture (HLA) within the W3C, in the context of ongoing discussions about making maps a first-class citizen of the Web. Hyper-Layering Architecture is not a new or purely theoretical concept. Its origins go back to discussions following the 1995 Great Hanshin–Awaji Earthquake, and it has been developed within the W3C community since the early days of SVG. The architecture was formally submitted to W3C in 2011, later reflected in SVG specifications, standardized domestically as JIS X 7197:2012, and has been operated in real-world systems for more than 15 years. Today, HLA 2.0 (Layers as Web Apps) forms the foundation of large-scale disaster information systems, including a recently launched public service. A draft Community Report summarizing the architecture and its background is available here. *1

Context within the Maps for HTML Community Group
At the same time, the Maps for HTML Community Group has been exploring MapML and related technologies, with the shared aspiration of making maps more native to the Web platform. During recent discussions—particularly around TPAC 2025—we agreed that creating a new Community Group was unnecessary. Instead, it felt more constructive to continue this exploration within the Maps for HTML Community Group, where complementary but different perspectives on Web mapping already exist. As these conversations progressed, an important point became clear.

Two Approaches, One Aspiration
MapML and Hyper-Layering Architecture share a broadly similar aspiration, but they approach it from different directions.

• MapML focuses on declarative, data-level interoperability within HTML.
• Hyper-Layering Architecture, by contrast, focuses on composing entire Web applications and services into a shared spatial context, treating the Web itself as a distributed map.

Rather than concluding in advance how these approaches should be unified, I began to explore a related question: whether it might be useful to identify a smallest shared foundation that could be discussed independently of any single specification. We agreed that this question itself is worth open discussion within the Maps for HTML Community Group.

Extending the Question
This question extends beyond MapML and Hyper-Layering Architecture alone. What is the minimal concept shared not only by these two approaches, but also by widely deployed ecosystems such as Google Maps, Leaflet, OpenLayers, D3, and even the many existing Web pages that already convey spatial meaning? That line of inquiry led to what I call the Minimal Map Model.

The Role of the Minimal Map Model
The Minimal Map Model does not attempt to define map formats, rendering pipelines, or application logic. Instead, it focuses on the most basic relationship between a region in CSS coordinate space and the geographic coordinates it represents. By intentionally limiting its scope, it aims to remain neutral with respect to existing frameworks and services, while providing a common reference point for discussion.
The Minimal Map Model is described in a separate exploratory draft. *2

Hyper-Layering Architecture itself already has working implementations and specifications, and continues to evolve through long-term practical use. From that perspective, this work is not a call for immediate standardization of HLA, nor a proposal to replace any existing specifications. The Minimal Map Model, by contrast, is presented as an exploratory contribution—intended to help clarify common ground and to support constructive discussion across different mapping approaches.

Looking Ahead
We hope that continuing this discussion within the Maps for HTML Community Group will help connect these perspectives, and contribute to a more open, user-centric, and interoperable future for Web mapping.

Further details are available in the following draft reports:
*1: Hyper-Layering Architecture — Community Report (Draft)
https://svgmap.org/movie/TPAC2025/HyperLayeringArchitectureCommunityReport.html
*2: A Minimal Map Model — Community Report (Draft)
https://svgmap.org/movie/TPAC2025/minimalMapModel.html