2.1.  Geographic Information Development by Municipalities

The main stakeholders in 2D geographic data development in Japan are municipalities. Municipalities generate various geographic information across different domains based on relevant legislation. For example, urban planning maps are developed based on the City Planning Act, road register maps are created in accordance with the Road Act, and housing status maps are produced under the Local Tax Law.

Particularly in the field of urban planning, each municipality conducts urban planning basic surveys and develops urban planning base maps that cover the entire city. The urban planning basic survey is a statistical survey conducted by municipalities based on the City Planning Act. Since the enactment of the act in 1968, each municipality has conducted the survey approximately every five years. Additionally, the act stipulates that municipalities must create urban planning maps. The background map used for these urban planning maps is known as the urban planning base map, which municipalities develop or update about every five years as well.

In this way, each municipality develops geographic information based on relevant legislation. The geographic information developed by these municipalities is considered to exhibit high completeness and reliability, with sustainable maintenance.

2.2.  Digital Transformation of Geographic Information in Municipalities

In the 1970s, forward-thinking municipalities introduced GIS (Geographic Information Systems) for specific applications such as urban planning and road management, and its adoption gradually expanded to other municipalities. However, the Hanshin-Awaji Earthquake in January 1995 accelerated the digitization of geospatial information, as relevant ministries and municipalities struggled to share geospatial data.

In the early 2000s, the Ministry of Internal Affairs introduced the concepts of “Integrated GIS” and “Shared Geospatial Data,” which enable cross-departmental utilization of geographic data within municipalities. The ministry issued guidelines to promote their implementation and established a subsidy program to support part of the implementation costs. This subsidy system continued for more than 15 years, resulting in an increase in the percentage of municipalities adopting Integrated GIS from 33.1% (579 cities) in 2010 to 65.9% (1,142 cities) in 2023. The guidelines and financial measures to promote them significantly contributed to the digitization of geospatial data in municipalities.

2.3.  Geographic Information Standardization

The Geospatial Authority of Japan (GSI), the national mapping agency of Japan, started working on the implementation of geospatial data standards from the late 1990s, in response to the international standardization activities by ISO/TC211 and OGC. Similarly, as mentioned previously regarding the promotion of digitalization triggered by the Hanshin-Awaji Earthquake, the importance of data standardization was also recognized.

Therefore, in 2005, the GSI established the Japan Profile of Geographic Information Standards (JPGIS) to promote standardization of geospatial data in Japan. JPGIS is a profile that extracts practical elements from the relevant ISO 19100 series standards necessary for creating geospatial data, particularly those related to data product specifications. Since then, Japan has adopted JPGIS as the implementation standard for geospatial data.

The GSI also adopted JPGIS to the “Guidelines for Public Survey,” which apply to survey works conducted by national and local governments. In addition, the GSI established standard product specifications for outputs of public surveys, such as digital topographic maps, resulting in each national and local government creating their data product specifications in accordance with JPGIS for public survey works.

On the other hand, various fields, including urban planning, developed data product specifications based on JPGIS to promote data standardization. However, each field created different application schema, and no GIS software could handle XML format data, which hindered the implementation of their data product specifications.

2.4.  Building NSDI

The “Basic Act on the Advancement of Utilizing Geospatial Information” (NSDI Act, which stands for National Spatial Data Infrastructure) was enacted in 2007. This act is a fundamental law that aims to promote the advanced utilization of geospatial information and establishes policies to form an NSDI as well as to promote the utilization and distribution of geospatial information.

Starting in 2008, the GSI began developing and providing Fundamental Geospatial Data (FGD) as part of NSDI. The FGD includes 2D GIS data, Digital Elevation Models (DEMs), and Geoid Models. The GSI creates the GIS data by integrating data collected from municipalities, such as urban planning base maps. The FGD serves as a positional reference framework for digital maps across the entire country and is available for free. The GSI supplies the 2D GIS data and Digital Elevation Models (DEMs) in GML format, while the Geoid Model conforms to the standard format defined by the International Service for the Geoid (ISG).

The GSI implements FGD based on a unique application schema created. Therefore, the encoding specification for FGD also utilize the GML Schema developed by the GSI. However, the GSI have developed and released a viewer and a converter to other GIS formats that are compatible with this encoding specification, and both commercial and free GIS software have added support for loading FGD. As a result, many users from industry, government, and academia extensively utilize FGD.

2.5.  Open Data and Geospatial Information Center

In July 2012, the Cabinet Office IT Comprehensive Strategy Office of Japan established the “Open Government Data Strategy” and has been promoting the disclosure and reuse of data held by municipalities and other entities. A basic policy titled “Easy Use of Public and Private Sector Data Held by the State and Local Public Entities” was defined in Article 11 of the Basic Act on the Formation of an Advanced Information and Telecommunications Network Society. This principle, aimed at making all data owned by the government public—including the data that serve as the foundation for policy planning—was articulated in 2017 under the concept of “Open Data by Design.”

In response to the trend of open data, various ministries and municipalities have been promoting the provision of their geospatial data. However, the proliferation of multiple data portals can hinder the convenience of data users. Therefore, the “Geospatial Information Center” was established as a platform to consolidate diverse geospatial data provided by various entities, both public and private, allowing users to search, download, and utilize the data in a one-stop manner.

The Geospatial Information Center was established based on the Basic Act on the Advancement of Utilizing Geospatial Information and outlined in the Second Basic Plan for the Advancement of Utilizing Geospatial Information (approved by the Cabinet in 2012). The plan aims to build an information center that facilitates the sharing and provision of geospatial information in Japan through the collaborative efforts of national and local governments, private businesses, and other stakeholders. The center began operations in 2016, with over 700 organizations from industry, government, and academia providing data through the Geospatial Information Center as of 2025.

3.1.  Adopting Standards

PLATEAU defines a data product specification (hereafter referred to as DPS) that is applicable to all municipalities in Japan. This is because PLATEAU recognizes each municipality as a key stakeholder in the development and updating of 3D city models. In Japan, there are over 1,700 municipalities, and if each creates its own 3D city model independently, there could be 3D city models based on more than 1,700 different DPSs. If the DPSs differ for each city, the reusability of the data decreases. Therefore, the City Bureau of the MLIT has developed a common DPS for 3D city models, named the Standard Data Product Specification for 3D City Models (hereafter referred to as the “3D City Model Standard DPS”). Subsequent references to this document will use the term “3D City Model Standard DPS.”

PLATEAU adopted the OGC standard “CityGML 2.0” as the application schema and the encoding specification for the 3D City Model Standard DPS to ensure interoperability among 3D city models while also addressing the needs of various cities. Although PLATEAU could have developed a proprietary application schema, this approach would have been time-consuming and would have required the development of tools from scratch to handle 3D city models based on that schema. Consequently, PLATEAU decided to adopt CityGML 2.0, which incorporates the expertise of specialists from various countries and has already gained acceptance in advanced cities around the world.

The international standard “CityGML” brings PLATEAU advantages described from the following four perspectives below.

CityGML is a standard for the data model and exchange format for describing, managing, and exchanging 3D city models. This standard conceptualizes a city from a semantic perspective, focusing on what comprises a city. One of the key functions of CityGML is the Level of Detail (LOD) system, which allows a single feature to have geometries at varying levels of detail, as well as an extensibility mechanism known as Generics module and Application Domain Extensions (ADEs) that enables applications across various fields and purposes. By utilizing this LOD and extensibility mechanism, each city can standardize semantics while selectively choosing the information necessary for its specific use cases.

In 2021, the CityGML 3.0 Conceptual Model was published, followed by the encoding specification in GML in 2023. However, PLATEAU began its project in 2020 and has been operating on CityGML 2.0 to date.

3.2.  Urban Planning ADE

CityGML provides definitions for basic features and their properties, while each domain can extend the model by incorporating detailed information tailored to specific purposes through ADE mechanism. In PLATEAU, the Urban Planning ADE serves to extend CityGML for describing the data necessary for various use cases.

Urban Planning ADE is an ADE developed by the Cabinet Office Secretariat for Promotion of Regional Revitalization. The ADE aims to structure the information necessary to serve an information platform for visualizing urban plans, measures for urban revitalization, and their results (i-Urban Revitalization). This ADE allows users to describe the results of the Urban Planning Survey, which is conducted periodically by the municipalities mentioned in section 2.1, as standardized features and properties. As a result, the Urban Planning Survey outcomes for each city, once used independently, can now be visualized within 3D city models and easily integrated or compared with those of other cities.

PLATEAU has adopted this Urban Planning ADE as well as CityGML from the beginning of the project and gives feedback on the results of use case development to the Urban Planning ADE every year. This feedback loop works as follows: Each city develops 3D CityGML using CityGML and Urban Planning ADE to realize its use cases. If they need any features and properties not defined in either CityGML or the ADE, they use the Generics module. Then, PLATEAU generalizes and structures those missing features and properties and the Cabinet Office reflects the generalized and structured features and properties into the Urban Planning ADE. Finally, PLATEAU updates the 3D City Model Standard DPS to refer to the updated Urban Planning ADE to use the ADE in the next year’s 3D city model and use case development. This feedback loop (Figure 1) repeats every year to reflect the user needs of various cities, enhancing the comprehensiveness and practicality of the Urban Planning ADE.

Figure 1 — Feedback Loop for Enhancing Urban Planning ADE

In addition, Urban Planning ADE was submitted as a discussion paper with consideration for the harmonization with CityGML and its contribution to the standards community.

3.3.  Standard Data Product Specification for 3D City Models

PLATEAU has developed the 3D City Model Standard DPS aiming to apply to 3D city model development for all municipalities in Japan. This DPS complies with the ISO 19100 series, adopting CityGML and Urban Planning ADE as its application schemas and covering all items necessary for data development, such as the coordinate reference systems, quality requirements, and data quality evaluation methods.

Particularly, since data creators for each city may differ, ensuring data homogeneity across the entire Japan is difficult. Therefore, PLATEAU not only defines the DPS as strictly as possible but also supports users in easily understanding the quality of 3D city models and using them.

3.3.2.  LOD Refinement

CityGML 2.0 defines five levels in LOD: The coarsest level LOD0 is a two and a half dimensional Digital Terrain Model over which an aerial image or a map may be draped. LOD1 is the well-known blocks models with flat roof structures. In contrast, LOD2 has differentiated roof structures, and thematically differentiated boundary surfaces; furthermore, LOD2 may have outer installations. LOD3 denotes architectural models with detailed wall and roof structures potentially including openings. LOD4 completes a LOD3 model by adding interior structures.

Figure 2 presents building models in LOD2 created in two different cities in 2020, the first year of the project. The building depicted in Figure 2 for City A features roof installations and accurately captures the intricate geometries of the wall surfaces. In contrast, the building in City B omits roof installations and presents a simplified representation of the wall surfaces. Both building models meet the definition of LOD2 and are valid models at this level. However, the simplified model from City B cannot adequately support applications requiring detailed models, such as that of City A. Conversely, supplying a detailed model like that of City A to applications designed for simpler representations, like that of City B, may result in excessive data volume and subsequent operational challenges. Both detailed and simplified LOD2 building models possess distinct advantages and disadvantages, making the assertion of the superiority of one over the other difficult. The key factor is to establish a consensus on the definition of LOD2 between data providers and data users. This mutual agreement is essential for ensuring effective communication and utilization of the data in various applications.

 

Figure 2 — Examples of variations in shape reproducibility within the same LOD

Consequently, to ensure mutual understanding among relevant stakeholders, PLATEAU has made a clear definition of each feature for each LOD. Furthermore, the subdivision of the LODs is introduced in the 3D City Model Standard DPS based on the research of Biljecki et al.　LODs are subdivided based on data owned by municipalities, since are designated as the responsible entities for maintenance to ensure sustainability (Figure 3). Specifically, municipalities can create LOD0, LOD1 and LOD2 using their aerial photographs or aerial laser point cloud data, thereby encompassing the entire city. LOD3 can be derived from data specifically acquired for individual use cases, primarily comprising images and point cloud data obtained through Mobile Mapping Systems. Furthermore, highly detailed LOD3 and LOD4 representations assume the use of Building Information Modeling (BIM) data.

 

Figure 3 — LOD subdivisions for LOD2 and LOD3

Figure 4 represents examples of each LOD subdivisions. In the LOD2 subdivisions, as the LOD increases, the roof shapes become more detailed, and the classifications of installations become more specific. In the LOD3 subdivisions, the increasing LOD captures smaller openings, while detailing from the side includes recesses and overhangs. In contrast, LOD2 does not represent recesses and overhangs.

The definitions of each LOD subdivision serve as a guideline for data creators when producing data. This allows them to create data that is consistent and tailored to requirements, avoiding both overly detailed and overly simplified datasets. Additionally, for data users, these definitions serve as a criterion to assess whether the quality meets their requirements, leading to an enhancement in the reusability of the 3D city models.

 

Figure 4 — Examples of LOD subdivisions

PLATEAU has set the default subdivisions of LODs as “LOD X.0” and each municipality can select the appropriate subdivision for their use cases. The quality attributes of each feature defined in the Urban Planning ADE describe the selected LOD subdivisions, allowing users to understand the applied subdivision. In this way,