D-Lib Working Groups

Metadata for Spatially Referenced Objects

Michael F. Goodchild
Alexandria Digital Library
University of California
Santa Barbara, CA 93106-4060
(805) 893-8049
(805) 893-7095 FAX
good@ncgia.ucsb.edu

On November 8, 1995 the Alexandria Digital Library at the University of California, Santa Barbara was host to an invited workshop on metadata. Geospatial data was used as an example, but the workshop studied metadata for all types of information in the digital library.

The following notes were prepared as an introduction to the meeting. See also the slides that summarize the results of the meeting.

Contents

Alexandria Digital Library

A digital library for spatially referenced objects:

  • referenced to a 2D (3D) frame
  • the geographic frame
  • geographic objects - maps, images, atlases
  • geographically referenced objects
  • the geographic footprint as an access mechanism

    • Geospatial metadata

    The Context:

  • map library cataloging
  • Federal Geographic Data Committee
  • TC 287

    • Problems:

  • continuous, hierarchical frame
  • 2 modes of addressing - coordinates, named places

    • Granularity:

  • analogs of books: map sheets, 9x9 images
  • atlases, encyclopedias, images embedded in books

    • Reducing granularity:

  • level of homogeneous description
  • object class
  • homogeneous semantics
  • homogeneous topological dimension
  • field
  • z(x,y) defined for all x,y
  • semantics of z
  • digital representation
  • topographic map
  • one or two fields
  • many classes of objects
  • image
  • one field, no objects
  • Open Geodata Interoperability Specification
  • field/object class
  • Rand McNally Road Atlas
  • 200 plates
  • 200x10 object classes, 200x1 fields

    • Increased granularity:

  • seamlessness
  • Encarta atlas
  • mosaic of imagery
  • map of metadata
  • multiple mosaics

    • Objectives of metadata

    Function:

  • allow the user to find, access information objects, assess their fitness for use
  • abstraction of object's content
  • information needed to assess fitness and not
  • available in the object
  • information needed to assure successful handling
  • production control functions
  • internal to producing agency

    • Issues

    User's description of need

  • no object will exactly match need

    • Producer's description of object

  • metrics of goodness of fit
  • 1. Assumes common language of description advanced user - SAP
  • 2. Assumes producer's description can be made domain- independent
  • need for content-based search

    • The map library user

  • needs expert assistance
  • lack of shared language of description
  • process of transformation
  • language of request
  • language of map library/map librarian

    • Models

    Transformation

  • changes language - 1:1
  • can be hidden
  • adds specification
  • must be emulated

    • Metaphors

  • card catalog
  • holdings control
  • uniform language
  • flat file

    • Surrogate expansion

  • single greek letter
  • Rand McNally Road Atlas
  • DLG, DEM, DOQ, DCW, ...
  • Landsat, SPOT, AVHRR, ...
  • economical surrogates
  • costly expansion
  • specialized data
  • no surrogates
  • value of expansion

    • Hierarchy

  • defined by economy of language
  • level of abstraction
  • multiple levels of communication
  • lowest level
  • OGIS granularity
  • highly structured
  • highest level
  • codes, TLAs
  • unstructured
  • links between levels

    • Analog/digital transition

  • different granularities
  • different high level languages
  • analog as persistent metaphor

    • FGDC and TC287

  • more or less complete specification
  • as high as possible
  • catalog metaphor/production, collection control lifetime?

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    Last revised: February 5, 1996