Spatial Metadata

1 Introduction

Metadata is often understood as “data about data”. It does not matter whether the data is digital or not. Such metadata includes information such as who owns it, where it came from, how was it measured, when was it produced, how good is it, and many other types of information. This note mainly introduces the importance of metadata and the metadata standards, Dublin Core and Spatial Metadata.

2 Importance of (Standardized) Metadata

The various aspects of metadata are carriers of important information, as indicated in the following table. The absence of such metadata could render the associated data (near) useless.

Table1. Various Aspects of Metadata

However, it is not generally sufficient to capture such metadata if it is going to be represented in an ad-hoc, non-standardized form. There should at least be a reasonably sized community of interest that should agree on what metadata aspects need capturing, their format, and a vocabulary that allows for the description of these metadata aspects. Such standardized metadata can then allow:

• Effective and efficient access to data by using the standardized formats and vocabulary;
• Discovery of relevant data.

There are 2 aspects of a metadata standard:

Table2. 2 Aspects of a Metadata Standard

3 Dublin Core

The Dublin Core Metadata Initiative (DCMI) is an organization dedicated to promoting the widespread adoption of interoperable metadata standards and developing specialized metadata vocabularies for describing resources that enable more intelligent information discovery systems. It provides simple standards to facilitate the finding, sharing and management of information. DCMI does this by (1) developing and maintaining international standards for describing resources, (2) supporting a worldwide community of users and developers, and (3) promoting widespread use of Dublin Core solutions.

The major characteristics of DCMI as an organization are (1) Independent: DCMI is not controlled by specific commercial or other interests and is not biased towards specific domains nor does it mandate specific technical solutions; (2) International: DCMI encourages participation from organizations anywhere in the world, respecting linguistic and cultural differences; and (3) Influenceable: DCMI is an open organization aiming at building consensus among the participating organizations; there are no prerequisites for participation.

The development and maintenance of a core set of metadata terms continues to be one of the main activities of DCMI. In addition, DCMI is developing guidelines and procedures to help implementers define and describe their usage of Dublin Core metadata in the form of Application Profiles. In essence, the Dublin Core Metadata Element Set is a suite of semantic definitions of 15 descriptive elements, specifically intended to support electronic resource discovery. The elements represent a broad interdisciplinary consensus about the core set of data elements that are likely to be generally useful in supporting online resource discovery. Dublin Core does not impose a controlled vocabulary. Instead it specifies that descriptive information about the content or other attributes of the entity being described – e.g. its author, language and date of creation - can appear in particular fields (the ‘elements’) in a particular format.

The primary 15 elements of Dublin Core Metadata are described as follows.

1. Title: a name given to the resource, typically the name by which it is formally known.
2. Creator: the entity primarily responsible for making the content of the resource (eg the individual author, organization or service).
3. Subject & Keywords: topic of the resource content, typically expressed as keywords, key phrases or classification codes from a controlled vocabulary or formal classification scheme.
4. Description: an account of the content of the resource, such as an abstract, table of contents or a free-text description.
5. Publisher: the entity responsible for making the resource available (eg an individual, organisation or service).
6. Contributor: an entity responsible for making contributions to the content of the resource, eg a person, organisation or service.
7. Date: a date of an event in the lifecycle of the resource, for example when it was created, published or modified. DC recommended best practice is to use the ISO 8601 standard, eg YYYY-MM-DD, and W3C Date & Time Formats (W3CDTF).
8. Type: the nature or genre of the content of the resource, typically a value from a controlled vocabulary such as the DCMI Type Vocabulary.
9. Format: the physical or digital manifestation of the resource, of value in identifying hardware or software needed to display or operate the resource.
10. Identifier: the Resource Identifier, an unambiguous reference to the resource within a given context, such as the the Uniform Resource Identifier (URI) , the Digital Object Identifier (DOI) and the International Standard Book Number (ISBN) or Serial Number (ISSN).
11. Source: a reference to a resource from which the present resource is derived.
12. Language: the language of the intellectual content of the resource (expressed using the two- and three-letter primary language tags in RFC 3066 and ISO 639).
13. Relation: a reference to a related resource.
14. Coverage: the extent or scope of the content of the resource, typically, spatial location (a place name or geographic coordinates), jurisdiction (such as a named administrative entity) or temporal period (a period label, date or date range), drawing on a controlled geospatial vocabulary such as the Getty Thesaurus of Geographic Names (TGN).
15. Rights: rights management information about rights held in and over the resource, e.g. Intellectual Property Rights.

4 Spatial Metadata

ISO 19115 is a geo-spatial metadata standard developed by ISO/TC 211. ISO 19115 defines a comprehensive metadata model for geographic objects. ISO/TC 211 also defined a smaller set of core metadata elements. This core contains the minimum elements that satisfy the requirements of an ISO conformant metadata record. The ISO 19115 standard does not specify storage format, but XML schemas are under development for an XML encoding of it (in full or for specialized profiles).

ISO 19115 defines more than 300 metadata elements (86 classes, 282 attributes, 56 relations), most of which can be applied optionally. At the topmost level the classes (or entities) are grouped in 14 packages (the "root" "Metadata entity set information" plus 13 dependent packages). Among the 14 top level packages of ISO 19115. Only the first two packages are mandatory indicated while the remaining packages are optional or conditional.

The mandatory and conditional elements of the ISO 19115 standard include:

Table.3 ISO 19115 elements

Though ISO 19115:2003 is applicable to digital data, its principles can be extended to many other forms of geographic data such as maps, charts, and textual documents as well as non-geographic data.

4.1 Geonetwork

GeoNetwork opensource is a standardized and decentralized spatial information management environment, designed to enable access to geo-referenced databases, cartographic products and related metadata from a variety of sources, enhancing the spatial information exchange and sharing between organizations and their audience, using the capacities of the internet. This approach of geographic information management aims at facilitating a wide community of spatial information users to have easy and timely access to available spatial data and to existing thematic maps that might support informed decision making.

Current version 2.1 of Geonetwork supports for metadata based on the ISO19115, FGDC and Dublin Core standards. This support includes:

1. storing and indexing of metadata in its original format
2. displaying search results in a uniform way
3. searching through the metadata in a uniform way
4. editing the different metadata standards online in default, advanced and XML mode
5. access to the full set of ISO19115 and FGDC metadata elements through the generic online editor
6. validation of metadata based on XSD schema's
7. import of XML formatted metadata and possible conversion of the input file through XSL transformation
8. batch import of XML formatted metadata and possible conversion of the input files through XSL transformation
9. generating of small and large thumbnails based on an input file in JPEG, PNG or GIF format (ISO19115 only).

Figure1. A snapshot of login interface of Geonetwork

There are several projects that use Geonetwork to management data. One of them is BlueNet. The goal of the BlueNet project is to establish a national distributed marine science data network linking universities to the AODC, to support the long term data curation requirements, and data access needs of Australia’s marine science researchers.

Development of the metadata entry and search tool, commonly referred to as the MEST, is a central component of the BlueNet strategy. The descriptive information gathered by this tool is based on ISO19115 for the development of geo-spatial metadata records, but also includes many marine-specific fields, as well as controlled subject-headings which are broader than marine. The first version, to address immediate BlueNet needs, is based on Geonetwork.