CHAPTER 4

The Architecture of the CGDI

The architecture of the Canadian Geospatial Data Infrastructure is similar to those of electrical power infrastructures and other data infrastructures. This chapter:

4.1 Spatial Data Infrastructures

The term spatial or geospatial data infrastructure (SDI) is often used to denote the relevant base collection of technologies, policies and institutional arrangements that facilitate the availability of and access to spatial data. The Global Spatial Data Infrastructure (GSDI) describes infrastructures in the following manner:

The spatial data infrastructure provides a basis for spatial data discovery, evaluation, and application for users and suppliers within all levels of government, the commercial sector, the non-profit sector, academia and by citizens in general.

The word infrastructure is used to promote the concept of a reliable, supporting environment, analogous to a road or telecommunications network, that, in this case, facilitates the access to geographically-related information using a minimum set of standard practices, protocols, and specifications. Like roads and wires, a spatial data infrastructure facilitates the conveyance of virtually unlimited packages of geographic information . . . Like roads and wires, a spatial data infrastructure facilitates the conveyance of virtually unlimited packages of geographic information.

A spatial data infrastructure must be more than a single dataset or database; it includes geographic data and attributes, sufficient documentation (metadata), a means to discover, visualize, and evaluate the data (catalogues and web mapping), and some method to provide access to the geographic data. Beyond this are additional services or software to support applications of the data. To make a spatial data infrastructure functional, it must also include the organizational agreements needed to coordinate and administer it on a local, regional, national, and or trans-national scale.

The creation of specific organizations or programs for developing or overseeing the development of spatial data infrastructures, particularly by governments at various scales, can be seen as the logical extension of the long practice of coordinating the building of other infrastructures necessary for ongoing development, such as transportation or telecommunication networks (http://www.gsdi.org/pubs/cookbook/chapter01.html).

4.2 Anatomy of an Infrastructure

To understand the architecture of the CGDI, it is useful to consider the anatomy of another common infrastructure: electricity. Any electrical power infrastructure has three main components:

  1. Suppliers: Those who supply electrical power to the infrastructure.

  2. Users: Those who consume electrical power. Users consume electrical power for a variety of different purposes, many of which were not conceived when the infrastructure was created.

  3. Interconnection Medium (link): The connections between the suppliers and users. Suppliers generate electricity in a variety of manners (e.g. nuclear, hydroelectric), and users consume electricity for different purposes. What allows all parties to work together successfully are the standards embodied in the interconnection medium. Of course, for the infrastructure to be successful, some initial investments must be made in building the link.

Figure 3 The Interconnection Medium

Figure 3 The Interconnection Medium

The general description of any electrical power infrastructure does not focus on specific suppliers or users of electricity, given the diversity of both, but rather on the standards and interconnection mechanisms that allow them to interoperate. This is a general feature of all infrastructures.

Spatial data infrastructures have many similarities to electrical power infrastructures. Users and suppliers exchange the infrastructure's "currency"; in the case of spatial data infrastructures, the currency is geospatial information. Like power infrastructures, the architecture of a spatial data infrastructure is best described in terms of the standards and interconnection mechanism and not the details of particular applications of its currency.

A spatial data infrastructure facilitates the flow of geospatial information between suppliers and users. Suppliers make data available through standard services, and users use the data and services to build applications. The infrastructure includes these services and applications, but the core architectural components are the standards and interconnection mechanisms that make the interoperability possible.

4.3 Components of the CGDI

Similarly, the core of the CGDI is the link that enables users to build applications from geospatial data and services made available by its numerous suppliers. With electricity, a network of electrical power lines connects suppliers and users; for its part, the CGDI relies on the Internet to interconnect its suppliers and users.

Both infrastructures, however, require standards of use. The electrical network in North America, for example, uses standards that allow anyone to safely plug a toaster into any outlet, knowing that it will deliver electricity at 110V 60Hz. However, different standards are used in Europe and North American toasters do not work there without adapters. In the same way, the CGDI uses standards that enable geospatial data to be easily exchanged over the Internet from suppliers to users. Specific CGDI standards are discussed in Appendix 1, CGDI-Endorsed Specifications.

Figure 4 Components of the CGDI

Figure 4 Components of the CGDI

4.4 Common Standards

Developing, maintaining and upgrading any type of infrastructure requires the coordinated efforts of many organizations. Implementing the foundation of a system, however, can often involve many different techniques. Just as an electrical power infrastructure is coordinated by multiple bodies, so too is the Canadian Geospatial Data Infrastructure. Despite this mixture, organizations are working together by using common CGDI-endorsed standards.

More specifically, the CGDI conforms to a published web services architecture in order to leverage the underlying information technology (IT) and infrastructure of the Internet along with ongoing developments in web service technology.

A web service is composed of reusable software components that encapsulate discrete functionality; it is distributed over standard Internet protocols. The functionality conforms to a defined interface and provides transparency to users as to how and where the service is implemented.

Within the CGDI, access to geospatial data is provided through web services. Various services have been defined for specific functions required by types of geospatial data, and for multiple access systems (e.g. "search metadata" versus "retrieve data").

In defining these services, the CGDI uses existing standards and specifications such as those from the United States Federal Geographic Data Committee (FGDC), International Organization for Standardization (ISO) 19100 series, and Open GIS® Consortium Inc. (OGC) standards and specifications. In this way, the CGDI is able to integrate and function with other federal, provincial, territorial, municipal and industrial geospatial infrastructures and initiatives throughout Canada and abroad.

4.5 Common Framework Data

The Canadian Geospatial Data Infrastructure facilitates the use of and access to all geospatial data. For instance, users have access to free framework data and with unrestricted use through the GeoBase portal (www.geobase.ca).

The CGDI also promotes sharing and compatibility of geospatial data by defining a common set of framework data. Framework data is the set of continuous and fully integrated geospatial data that provides context and reference information for the country. Framework data is expected to be widely used and generally applicable, either by underpinning or enabling most geospatial applications.

Framework data takes three principal forms:

  1. Alignment layers include geometric controls required to adequately position geospatial information. By themselves, these layers do not have representations of physical, economic or social phenomena, as will other framework layers or application specific layers, but these layers are critical to the reliability and use of all other layers.

  2. Land feature layers contain well-defined and readily observable natural or man-made physical features that are not subject to interpretation or speculation. These layers include many of the same features that are visible on topographic maps, such as roads, rivers and elevation. Although useful for some applications by themselves, they are also used to provide reference information for the conceptual layers.

  3. Conceptual layers are the frameworks that society develops and uses to describe and administer the country. These layers complement a vast amount of application specific data. They are often interpreted from observations of physical, economic or social factors, and include features such as municipal boundaries, federal electoral districts and ecological areas. Inclusion of any specific type of boundary under this layer is subject to its availability over large areas of the country, its geometric integration to alignment layers, and a consensus among major stakeholders on the importance of the presence of the data.

CGDI framework data has the following general characteristics:

Framework data comprises features that are composed of a geometric representation and their related attributes. Moreover, attributes are those that can provide context and reference information for the country, namely those that can either underpin or enable most geospatial applications. When applicable, toponymy (place names of a region) is one specific attribute of the features that compose framework data.

4.6 Joining the Global Spatial Data Infrastructure

As a result of these common standards and framework data, the Canadian Geospatial Data Infrastructure is able to join with other national spatial data infrastructures to form a global spatial data infrastructure, providing Canadian data and information suppliers with access to global markets. The Global Spatial Data Infrastructure describes the globalization of geospatial data infrastructures in this way:

Just as spatial data infrastructure programs necessarily involve the alignment of scarce resources for achieving success, so too it is necessary to ensure that spatial data infrastructure initiatives develop in harmony with each other in order to maximize the impact of these programs. In reality, many initiatives are working in isolation, not necessarily developing in harmony with others and consequently unable to reap the benefits of working together.

Anyone who is involved in a project of which spatial information forms an integral part and who intends leaving a legacy of spatial data or tools to exploit the data that lasts beyond the period of funding for the project is, by definition, participating in some of the fundamental elements required by a spatial data infrastructure. As coordination between such organizations expands, these projects very often lay the foundations on which initiatives formally dedicated to the establishment of spatial data infrastructures can then build.

At a global scale, the most prominent examples of formal spatial data infrastructure programs are on a national scale. Most of these are driven by national or federal governments (e.g. the NSDI in the USA, the SNIG in Portugal, Australia's ASDI, Malaysia's NaLIS, South Africa's NSIF, Colombia), but there are exceptions such as the Uruguay Clearinghouse and NGDF in the United Kingdom, which have largely been driven by the private sector.

In most cases the need for wide participation in the development of lasting, useful spatial data infrastructures is acknowledged, and so private-public partnerships are encouraged. The beneficiaries of spatial data infrastructures are generally seen to derive from the public and private sectors, academia and non-governmental organizations, as well as individuals. Federal countries are often able to build their national spatial data infrastructure programs on spatial data infrastructure programs being driven by provincial or state governments (e.g. the ASDI of Australia). Trans-national spatial data infrastructure initiatives often arise out of existing trans-national structures (e.g. the Permanent Committee for GIS Infrastructure in Asia and the Pacific was formed through the UN Regional Cartographic Conference for the Asia-Pacific region) (http://www.gsdi.org/pubs/cookbook/chapter01.html).

Joining the global spatial data infrastructure via the CGDI will provide Canadian data and information providers with access to global markets. This in turn provides users and organizations from around the world with access to Canadian data, services and organizations. A barrier-free geospatial infrastructure, at both the national and global levels, is of great economic and social benefit to Canadians. In short, a global geospatial data infrastructure will give Canadians a better view of the world and its issues.

Figure 5 Global Spatial Data Infrastructure

Figure 5 Global Spatial Data Infrastructure

 

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