12              Metadata

12.1              Many organisations have recognised the problems that error and uncertainties in spatial datasets can cause to potential users. They are compounded when there is no information available as to how, when or why a dataset was created, leaving the user blind to the quality of the data that they are using. In an attempt to overcome these problems and to provide at least a basic understanding of the quality of a given spatial dataset, the concept of Metadata has been developed (DeMers, 1997, p150, Burrough and McDonnell, 1998, p81 and ANZLIC, 1996).

12.2              “Metadata is data about data. It is a description of the characteristics of data that has been collected for a specific purpose.” (ANZLIC, 1996). Metadata usually describes the data that comprises a single spatial theme. If Metadata is present, a user can at least get a basic understanding of the quality of a spatial dataset and then ascertain the suitability of that dataset prior to utilising it.

12.3              A survey of National and Regional Spatial Data Infrastructure Activities around the globe was conducted in preparation for the Global Spatial Data Infrastructure GSDI meeting in Canberra Australia, in November 1998 (GSDI 3 Meeting). ‘The goal of this survey was to gather baseline information on the nature and characteristics of the national spatial data infrastructures (NSDI’s) currently being developed’ (Onsrud, 1999). Twenty-six nations and eleven Multi-Nation and Regional Initiatives responded to the questionnaire. The results of the questions pertinent to Metadata showed that the concepts of Metadata are well accepted as being key components of NSDIs around the world (Onsrud, 1999).

12.4              There are several approaches to the level of detail required to describe a spatial dataset within Metadata e.g. the approaches adopted by the US Federal Geographic Data Committee and by the Australia and New Zealand Land Information Council. ‘The US approach, developed by the Federal Geographic Data Committee (FGDC), specifies the structure and expected content of some 220 items (elements) which are intended to describe digital geospatial datasets adequately for all purposes.  The ANZLIC approach is deliberately less ambitious than what has been attempted in the US.  Arguments advanced in support of the more modest objective rely on experience to date with the creation of high-level directories in Australia.’ (ANZLIC, 1996).

12.5              The ANZLIC Working Group on Metadata developed the ANZLIC Metadata guidelines over a period of eighteen months. This process involved considerable consultation with organisations around Australia and New Zealand. The Guidelines allow for the description of spatial data at increasing levels of detail, from a set of ‘Core’ elements through to the specific details required by individual organisations. An example of some of the Core categories of information required to describe a spatial dataset using the ANZLIC Metadata guidelines are (ANZLIC, 1996):

12.5.1   Dataset title and custodian.

12.5.2    Dataset description.

12.5.3   Dataset currency (start/end date) and status (completed).

12.5.4    Stored and available GIS formats and any access restrictions (e.g. copyright, license restrictions etc).

12.5.5     Data Quality (Lineage, Positional and Attribute Accuracy, Logical Consistency, Completeness. These concepts are expanded upon in Chrisman 1991, pp169-172).

12.5.6    Contact Information and Metadata date.

12.6              Care needs to be taken when interpreting Metadata, as not all of the people who are responsible for compiling Metadata understand the issues involved, particularly those issues that relate to Lineage, Positional and Attribute Accuracy, Logical Consistency and Completeness. For example the question, ‘What does Logical Consistency mean?’ is often heard. If in doubt, contact the person nominated in the Metadata as being the point of contact.

12.7              Entity Based Metadata     In many instances Metadata about all of the spatial data that exists in a single spatial theme is insufficient to adequately describe the data in that theme. Metadata may be required that describes individual spatial entities. Some examples are:

12.7.1     A regional GIS stored in a Relational Database where topographic data has been obtained from several agencies.

12.7.2     A spatial dataset that records a particular geographic phenomenon as point features. The dataset is considered a live dataset in that information is being added on a continual basis, as new information becomes available. The phenomena may have been located over time using a variety of methods including:

12.7.2.1            Differential GPS,

12.7.2.2            Handheld GPS using GPS data corrupted by Selective Availability,

12.7.2.3            A map reference obtained by triangulation using known and readily identified features,

12.7.2.4            A map reference determined by dead reckoning,

12.7.2.5            A map reference obtained remotely in e.g. a helicopter.

12.8              A variation of the standard concept of theme based Metadata is required to adequately describe each individual entity in the above two datasets. Considering the second example above, entity based Metadata will allow for an audit of the dataset which may result in less accurate data being replaced over time with data captured using a more appropriate method. That is, assuming that the details of methods used to obtain each individual entity have been recorded.

12.9              It appears that these concerns are being catered for, as the proposed European Metadata standard CEN TC287, prENV 12656 includes the functionality to describe the quality of spatial data by theme, by subset of that theme or even by a single entity. It also appears that the proposed Metadata standard that is being developed by the International Standards Organisation’s TC211 may adopt this approach.

To make suggestions or corrections to this web page, please contact posacc@geoinnovations.com.au.
The information on this web page is © Copyright 1999 B.S.Bannerman.
All commercial rights reserved.

B.S.Bannerman materials published on the Internet are protected by copyright law. Apart from fair dealing for the purposes of private study, research, criticism or review, as permitted under the Copyright Act 1968, no part may be reproduced or reused for any commercial purposes whatsoever.

GeoInnovations Pty Ltd materials published on the Internet are protected by copyright law. Apart from fair dealing for the purposes of private study, research, criticism or review, as permitted under the Copyright Act 1968, no part may be reproduced or reused for any commercial purposes whatsoever.

Copyright © 1998, 1999, 2000 GeoInnovations Pty Ltd.
GeoInnovations is a registered Trade Mark of GeoInnovations Pty Ltd.
Last modified: March 15, 2000.

Send email to info@geoinnovations.com.au with questions or comments about this web site.