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Subject: Geographic Subject Coordinates investigation
Date: Wed, 22 Jun 2005
From: "Colleen R Cahill" <[log in to unmask]>
To: <[log in to unmask]>

        The Geography & Map Division of the Library of Congress is seeking those interesting in participating in an investigation for the developing a system of geographic coordinates based on geographic subject headings.  The goal of this is to permit standardized computer-searchable coordinates to be placed in electronic records to support Geospatial Information System graphic interfaces and make the search for items with geographic subject headings easier, faster and more reliable.

        Currently in the Library of Congress, geographic coordinates of cartographic materials are supplied in bibliographic records to describe the extent of the item. These coordinates, when supplied by a cataloger, are entered in the MARC 21 Cartographic Mathematical Data fields (255/034)*,  but for very practical reasons, there are some limitations to this data:

        1. Coordinates may not appear on a cartographic item: this means that catalogers must decide to leave this data out or gather the data from other sources. This process can be both time consuming and inexact

        2. The coordinate data might not be based on the Greenwich Prime Meridian (the coordinate system used on most maps throughout the world published since 1890 according to international convention) and converting these other geographic coordinate systems (meridians based on Washington D.C., Paris, Ferro Islands, Pulkovo, etc.,) to Greenwich equivalents is equally time consuming and, possibly, inexact. Non-conforming data would need to be converted or left out of the record

        3. Though the very idea of geographic coordinates is to provide a universal way to locate geographic features, the coordinates provided on the map may be unreliable or known to be incorrect.  The inclusion of incorrect coordinate geographic data in a bibliographic record may make that record equally suspect or useless

        4. The coordinates of a item might extend beyond the edges of the primary geographic location: for example, a map of Pennsylvania might also show parts of New York, New Jersey,  Delaware, Ohio, Maryland and West Virginia.  Currently, a system using coordinates to search for a map of Pennsylvania would locate this map; but the same map could also appear in searches for any of the neighboring states, even though only portions of those states appear on the map.

        In summary, while supplying geographic coordinates in a bibliographic record will greatly assist researchers' access, inclusion can be difficult and time consuming for some items and limiting in some searches. Additionally, geographic coordinates are currently limited to only cartographic materials but other formats may benefit from the ability to search geographic locations by coordinates.

        To address this issue, the Geography & Map Division would like to propose a supplement (not a replacement) of the coordinates currently used in bibliographic records with a field for standardized geographic coordinates of all geographic locations listed in the subject headings of an item.  Ideally, once these standardized geographic coordinates are defined, the advantages of this would be:

        1. Geographic coordinates can be placed in a record quickly
because
        2. A geographic authority database of coordinates could be created
and
        3. Require less experienced staff and less time per record to implement
plus
        4. Be applied to any item, regardless of format,  that has a geographic location in a subject
and
        5. When tied to a date or range of dates, can limit a geographic location to a specific era
which would
        6. Allow search engines and graphic interfaces to display data not only for a given area, but also for a certain time period

The new field would be in a computer-searchable form, as the basic information of geographic location and date are already available for human viewing or text searching in other fields (LC uses MARC 21 fields for place, publisher and date (260), as well as subjects (650, 651)).

The two basic pieces of information are the machine-readable coordinates and date(s).  Using MARC 21 fields as a starting model, the Coded Cartographic Mathematical Data (034 field) uses decimal information for the geographic coordinates.  The purposed field should follow the same format, as cartographic catalogers and some library systems already use coordinate data in this form, making training staff and programming searching easier. Also, many other systems can utilize this format,  such as ESRI's ArcView software.

Many of the geographic locations would be best served by having at least 4 sets of coordinates: westernmost longitude, easternmost longitude, northernmost latitude and southernmost latitude, as this would assist graphic search interfaces. Support of polygon coordinates could be added optionally.  There will exceptions to the use of 4 coordinates, such as in a city, which might be better represented with a center point coordinate. Also, coordinates from other planets will need to be identified and usable in these fields.

        In MARC 21, the Time Period of Content (045 field) captures data of what era the item covers. This MARC field would be useful for modeling the formatted date in the proposed field. The date field would help define the coordinates to the region they represent for a specific period.  There are many examples of regions, counties, territories, states, empires and other boundaries changing over time.  This field could also be applied to events, such as battles, human or animal migrations, or climatic data.

        There will be challenges in making this proposal a reality:

        1. Gathering the data
                -who will gather the data? (librarians, scholars, cartographers, government agencies, corporate entities, etc.)
                -who will authorize/maintain the data
                        G&M would like to see this data in the Library of Congress Authority Records for the geographic locations and events, but it could be stored elsewhere
        2. Establishing Metadata Standards
                -Models from existing standards:  MARC, FGDC, etc.
                -Use by other standards (i.e. EAD, Dublin Core, etc.)
                -Allow data to move between standards, as with crosswalks or other tools

        A large number of those interested in geographic access to materials, such as the scholarly community, the publishing community, and the library community may be interested in the purposed field, as its application goes far beyond cartographic materials.  The Geography & Map Division offers to facilitate discussion of this issue and hopes that this will include many libraries, colleges and universities, government agencies, creators of information,  publishers of all types of materials, national and international information and metadata organizations, and researchers. This "Coordinates for Geographic Subject Headings Working Group" could focus on defining standards for the data and the gathering and establishment of coordinates/dates for use in this new search tool.

        Anyone interested in joining in this endeavor can contact the Geography & Map Division Subject Coordinates Committee through Colleen Cahill (202-707-8540, [log in to unmask]).  While this is an ambitious undertaking, the Division knows with many participants will make it possible to create a truly useful search tool.


*More information on MARC 21 fields are available in the MARC 21 Format for Bibliographic Data and at the Library of Congress Cataloging Distribution Division website http://www.loc.gov/cds/marcdoc.html





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