Metadata and Geographical Information Systems

Adrian MossKINDS project,

Manchester Metropolitan University, UK

a.moss@mmu.ac.uk

The need for metadata

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Value of data

Value ofcomputers

As computing power becomes comparatively cheaper and mass storage space increases dataincreases in value. A method of cataloguing and managing data isneeded.

Uses of metadata to maintain an organisation's internal

investment in geospatial data, to provide information about an

organization's data holdings to data catalogues, clearinghouses, and brokerages

to provide information needed to process and interpret data to be received through a transfer from an external source

Visions

The Digital Earth: Understanding our planet in the 21st Century by Al Gore

Microsoft "Digital Nervous System" by Bill Gates

Although often such ‘visions’ do not explicitly mention metadata, yet it will be key to their development

Defining geospatial metadataA metadata record is a "surrogate" record which describes another information

resource. It can also be called "data about data".

The US Federal Geographic Data Committee, (FGDC), define metadata

as describing:

•availability -- data needed to determine the sets of data that exist for a geographic location.

•fitness for use -- data needed to determine if a set of data meets a specific need.

•access -- data needed to acquire an identified set of data.

•transfer -- data needed to process and use a set of data.

(Source: FGDC Content Standard for Digital Geospatial Metadata, CSDGM).

Applications for geo-spatial metadata

Finding spatial data

Transferring data from one system to another

Requesting a service from another computer

Types of metadata (1)

Collection level metadata – Content Overview of the contents of a data

collection

– Purpose Identifying potential data sources

Types of metadata (2)

Data set level– Content Description of the content of a

data set

– Purpose Evaluating the usefulness of data

Types of metadata (3)

Feature level– Content Detailed description of data and

features

– Purpose Interoperating Open Systems

Metadata formats:Example 1 The Dublin Core Widely used to describe ‘document like

objects’ Consists of 12 elements all of which are

optional and may be duplicated– Title, Author, Publisher, OtherAgent, Date,

ObjectType, Form, Identifier, Relation, Source, Language, Coverage

Highly flexible, but consequent lack of semantic and syntactic precision

Metadata formats: Example 2 The Content Standard for Geospatial Metadata Data set level metadata. Developed by

US Federal Geographic Data Committee Detailed, extensive record system

including:Overview Organization of the Standard 0 Metadata 1 Identification Information 2 Data Quality Information 3 Spatial Data Organization Information 4 Spatial Reference Information 5 Entity and Attribute Information 6 Distribution Information 7 Metadata Reference Information 8 Citation Information 9 Time Period Information 10 Contact Information

Review question 1

Components of a metadata system Metadata format

– The metadata implementation chosen as the basis for the system

Creation tools– Any automated methods of generating data

Transports– Methods for querying and transporting

metadata in a networked environment

Metadata in resource discovery systems Used to increase the accuracy of

resource discovery queries– Controlled vocabularies– Thesauri– Gazetteers

Controlled vocabularies

Defines words a terms that maybe used when cataloguing records– e.g.. Use river not stream

Often requires data to be catalogued by an expert librarian

Thesauri and dictionaries

Define relationships between termsRelationship Description Example

Hierarchicalrelationship

Defines narrower and broader termrelationships between terms

“Travel” is abroader term than “airtravel”

Associativerelationships

Defines similarity in meaningbetween terms

“Trip” is relaated to “travel”

Equivalencerelationships

Terms with the same meaning “Journey” is a non prefered term for“travel”

Gazetteers

Links place names to spatial locations KINDS Gazetteer

(http://midas.ac.uk/kinds) extends thesaurus relationships to describe relationships between spatial units

KINDS Gazetteer relationships

HierarchicalUnited Kingdom Is the top term for the hierarchy

‘census geography’City of Manchester Is contained within Greater ManchesterGreater Manchester Contains City of Manchester

Associative03BN(a census area ID code)

Is spatially coincident to Tile SD

03BN Is spatially coincident to Tile SJ

Equivalence03BN(a census area ID code)

Is the ‘preferred term’ for City of Manchester

City of Manchester Is a ‘non-preferred term’ for 03BN

Metadata creation tools

Creation tools are used to automate the creation of metadata

The requirement for creation tools increases as the level of detail in a metadata format increases

Finding data across data sets

In a distributed environment data and metadata will be held on different servers.– Z39.50 protocol allows searching of data

resources held on different servers Also metadata can be embedded in data

objects.– Embedding metadata in web pages– XML, eXtensible Markup Language

Z39.50 - a protocol for querying multiple index servers

A Z39.50 compliant client accepts a request and distributes it to multiple metadata index servers. The results are collated by the client and returned to the user as a single output

Client

Servers

Embedding metadata within web pages/data

<HTML>

<HEAD>

Metadata description of page

</HEAD>

<BODY>

Hyper-text lay out of page

</BODY>

</HTML>

Catalogued by search index

XML - Extend the internet XML eXtensible Markup Language permits definition of custom ‘tags’ for specific purposes.E.g. to describe the extent of a geographic data set.

<MINIMUM X="348304"><MINIMUM Y="234985"><MAXIMUM X="549854"><MAXIMUM Y="459054">

Enables direct communication of metadata between networked applications

The future of metadata in resource discovery systems Multiple metadata formats

– The Warwick Framework From static to dynamic surrogates

– Automatic generation of metadata based upon the users requirement

The Warwick Framework

A proposal to develop ‘packages’ of data which include: the data it self and one or more metadata descriptions of the data.

Response to the problem that no single metadata format is suitable for many requirements

Metadata and GIS support

Using GIS is a knowledge intensive activity. Users must learn the concepts associated with GIS and mapping, as well as how to work the GIS package itself. Often these tasks are complex and time consuming. GIS can be made much simpler to use if certain low level tasks could be devolved to the GIS package or if the GIS could provide advice to the user on best practice.

Plewe and Johnson (1997) report a system which reads metadata files and advises the user of quality issues associated with the data set being used.

Review exercise 2

Metadata and Open GIS (1)

Aims:– Transferring data from one system to

another (support with appropriate reformatting, or on-the-fly access to open systems based data bases)

– Requesting services from networked servers Led by Open GIS Consortium

(http://www.opengis.org)

Metadata and Open GIS (2)

Open GIS data structures created BUT, more serious intellectual problems

standardising geographical world views. Characterised by a lack of “global schemas”.

Conclusions Metadata being rapidly developed by

information scientists for resource discovery. – Dublin Core is becoming standard for “document

like objects”. DC support spatial and temporal fields.

Little formal support for metadata in commercial GIS software.

Open GIS has achieved technical success but standardisation of world views will be harder.

Control questions