The Library of Congress >> Especially for Librarians and Archivists >> Standards
HOME >> MARC Development >> Discussion Paper List
DATE: December 22, 2020
NAME: Coordinates for Geographic Positioning of Structures in Images in the MARC 21 Bibliographic Format
SOURCE: Canadian Committee on Metadata Exchange
SUMMARY: This paper discusses use cases for geographic positioning based on geographic coordinates of structures such as monuments, buildings and sites that are depicted in images and how to code this data in the MARC Bibliographic format.
KEYWORDS: Field 034 (BD); Coded Cartographic Mathematical Data (BD); Field 255 (BD); Cartographic Mathematical Data (BD); Geographic Positioning (BD); Geographic Coordinates (BD)
12/22/20 – Made available to the MARC community for discussion.
Geographic positioning (or geopositioning) is a process for pinpointing the geographic location of an object or structure and using those geographic coordinates to indicate that position with respect to a useful frame of reference. In a bibliographic context, this would mean providing geographic coordinates to link from a bibliographic record to an interface which presents data to end users geographically. Such interfaces can allow searching by location or browsing via a map interface and provide users with an innovative way to explore collections.
There are many ways to record geographic information in the MARC 21 formats, but most of these methods are at high levels of granularity. Without reviewing every such field, the principal ones use either place names or codes to indicate the location. The geographic area codes in field 043 are limited to the level of countries and in some cases states or provinces. Geographic subject headings in field 651, or geographic subdivisions in subfield $z of topical subject headings in field 650, provide access via the names of places, generally broadly at the level of countries, states or provinces, and may go to the city level of granularity, but rarely below that to the level of very specific features, structures, or locations that may be present in an image.
More precise pinpointing of a location requires recording geographic coordinates indicating longitude and latitude, rather than just place names. Certain types of collections lend themselves particularly well to requiring this level of precision in identifying the location referenced by the resource. Consider a collection of postcards depicting buildings, street views, parks, or public monuments in a city. Just giving the name of the city as the location will not distinguish the locations of the different sites nor provide any insight into the collection for users. Such an application requires geographic coordinates.
Subject analysis practices for image collections vary. Often access points are provided for the specific named structures depicted (such as a public monument or a named building), but depending on the policies of the subject authority file and granularity of the authorized access points available, it may not be possible to assign precise access points that usefully correspond to the location in an image. Images may depict unnamed structures, street views, street intersections, or portions of a larger named area (such as a view of a flower bed within a large park), which are unlikely to correspond to an established heading in a subject system. The overhead to create textual strings to uniquely describe such specific locations might not be considered practical in most subject systems. Such identification is also unlikely to meet any criteria for literary warrant required by a subject system before an authoritize access point is created. Because of this, image collections are often indexed with much more general headings that describe the category of thing depicted and the city or larger named areas where it is found. Such subject headings do not provide enough geographic precision to feed usefully into a geopositioning application. For this reason, this discussion paper does not pursue the solution of adapting existing subject fields 650 or 651 for geopositioning applications.
A current use case for geopositioning is provided by Bibliothèque et Archives nationales du Québec (BAnQ). BAnQ contributes digital images (e.g., archival photos, postcards, prints, posters) to platforms such as Historypin (https://www.historypin.org/en/) that provide access to images via a cartographic interface. This involves providing the geographic coordinates of the objects or areas represented on the images. To better manage and utilize this information, BAnQ would like to store it in the bibliographic records describing the images. This would also allow BAnQ to use the information in its own digital repository, BAnQ numérique (https://numerique.banq.qc.ca/).
While the interest and focus of the request is for applications involving image collections, other types of resources or collections may have a granular geographic focus. Possibly some textual collections that describe landmarks or buildings might be candidates for such treatment. If this need is actual rather than just theoretical, then the eventual solution should be broad enough to allow these use cases as well.
While an individual institution could always implement a local field for internal use, the geographic coordinates apply to all libraries holding the same material and could usefully be shared and communicated to other libraries. For this reason, an encoding solution within the communication formats is preferred.
Considerations reviewed above indicate that existing subject fields 650 (Subject Added Entry – Topical Subject) and 651 (Subject Added Entry – Geographical Name) are not at an appropriate level of granularity to satisfy the expressed need and are not explored further in this paper.
Two fields presently in the MARC 21 Bibliographic Format allow the recording of geographic coordinates, field 034 (Coded Cartographic Mathematical Data), subfields $d-$g,and field 255 (Cartographic Mathematical Data), subfield $c. The current definitions of these fields follow.
Field Definition and Scope:
Mathematical data associated with cartographic material, including celestial charts. This data may also be coded in field 034 (Coded Mathematical Data).
Data recorded includes a statement of scale, statement of projection and/or a statement of bounding coordinates. The coordinates can represent a bounding rectangle, the outline of the area covered, and/or the outline of an interior area not covered. For celestial charts, it may also contain a statement of zone, declination data, and/or right ascension data, and/or equinox.
Field Definition and Scope:
Contains cartographic mathematical data, including scale, projection, and/or coordinates in coded form. For digital items, the coordinates can represent a bounding rectangle, the outline of the area covered and/or the outline of an interior area not covered. For celestial charts, it may also contain zone, declination data, and/or right ascension data, and/or equinox. There should be an 034 field corresponding to each 255 field in a record.
Field 255 (Cartographic Mathematical Data) provides mathematical data for cartographic material, such as a map, including its coordinates, in a format intended for display to end-users. It usually defines the area covered by the map as a bounding box and therefore helps users identify the resource they are looking for or choose one that is appropriate to their needs (e.g., that covers the appropriate area). Field 255 does not provide specific content designation for latitude and longitude because it is not necessary for display purposes. The orientation of this field for public display is confirmed by considering the definition of subfield $c as a Statement of coordinates, and the reference to ISBD display. This lack of granularity and the necessity to parse the data reduce the potential of field 255 subfield $c for machine manipulation of geographic coordinates data, and make it an unlikely candidate for a geopositioning application.
$c - Statement of coordinates (in field 255)
Coordinates are recorded in the order of westernmost longitude, easternmost longitude, northernmost latitude, and southernmost latitude.
In records formulated according to ISBD principles, subfield $c data are enclosed in parentheses. The two longitude statements and the two latitude statements are each separated by two hyphens (--). The longitude is separated from the latitude by a slash (/).
Field 034 (Coded Cartographic Mathematical Data) is intended to complement field 255 by providing a coded version of the mathematical data for cartographic materials, in a form more amenable to machine manipulation. This is evidenced by the use of four subfields $d-$g defined to record the latitude and longitude values needed to define a bounding box. The conventions for recording the coordinates in a standard fashion are given after subfield $g as follows.
Subfields $d, $e, $f, and $g individually identify the four coordinates of the item. Subfield $d represents the westernmost extent of the item; subfield $e, the easternmost extent; subfield $f, the northernmost extent; and subfield $g, the southernmost extent. The abbreviations for the hemispheres are: N = North, S = South, E = East, W = West.
Subfields $d, $e, $f, and $g always appear together. The coordinates may be recorded in the form hdddmmss (hemisphere-degrees-minutes-seconds), however, other forms are also allowed, such as decimal degrees. The subelements are each right justified and unused positions contain zeros.
The convention for recording a centre point instead of a box is also given and consists of repeating the West-East and North-South coordinates. This lends itself well to recording geographic coordinates for granular features such as specific buildings, monuments, squares, or similar.
If the coordinates for a map or plan are given in terms of a center point rather than outside limits, the longitude and latitude which form the central axis are recorded twice (in subfields $d and $e and in $f and $g, respectively).
However, both fields 255 and 034 are restricted to cartographic material, while the application to geographical positioning would be primarily in records describing images or other visual material. One solution would be to broaden the definition of field 034 in the Bibliographic format and provide usage guidelines so that it can be used to record geographic coordinates for any relevant type of materials.
Field 034 is also defined in the Authority format, which could be used instead of the Bibliographic format for some applications, when the feature or structure to be positioned is the focus of an authority record. The scope of field 034 in the Authority format seems less restrictive than in the Bibliographic format in that the coordinates would relate to the entity in the 1XX of the authority record, whatever that entity is.
From the 034 Field Definition and Scope in the Authority Format:
Coded form of the cartographic mathematical data relevant to the geographic aspect of the entity in the 1XX. The data that is recorded usually derives from authoritative sources.
An alternative option would be to define a field specifically for geographic coordinates relating to images and visual materials, which would include four subfields that would parallel subfields $d-$g from field 034. However, there are not many fields available in the 0XX numbers and codes block in both the Bibliographic and the Authority formats. Possibly another block is more appropriate than 0XX, such as maybe 6XX. Defining multiple fields in the format to carry geographic coordinates with definitions that vary solely on the format of the material being described may seem redundant to many, and also to run counter to the format integration process that brought the separate formats together in the single Bibliographic format we have today.
To pursue the option of broadening field 034 (Coded Cartographic Mathematical Data) to extend its usage to images would require at minimum an additional paragraph in the Field Definition and Scope. Since presently field 034 is used in concert with field 255, usage guidelines for applying only the geographic coordinates subfields of field 034 to image materials without the concomitant field 255 would be needed.
It could also be helpful to add to the usage guidelines under 034 subfield $g to explain that the convention of coding for a centre point is to be used when coding a small feature or structure. Finally, adding appropriate examples of this usage, under subfield $g, would be helpful.
The addition to the Field Definition and Scope could be as follows:
For images or graphic materials, geographic coordinates are recorded to represent the position of the structure, site or feature depicted in the resource. In this case, field 034 does not have a corresponding field 255 in the record.
BIBFRAME accommodates the information relating to cartographic materials and if a change to MARC is needed the expectation is that it would not be difficult to accommodate.
6.1. Is the use case for recording geographic coordinates in bibliographic records for specific features represented in images clear?
6.2. The discussion paper proposes expanding the use of coordinates to non-cartographic images, are there other content types that might benefit from the same treatment (e.g., a book describing a building)?
6.3. Is there a need to provide a solution applicable to authority records as well as bibliographic records?
6.4. Is field 034 a suitable field in which to code this data, in both the Bibliographic and the Authority formats, or is a new field preferred? If so, in which block of the format should this field be?
6.5. Does the proposed text for the 034 Field Defintion and Scope clearly explain the proposed usage?
6.6. Are there any other possible solutions that might be explored to accommodate this use case? For example, if field 034 is not suitable for this purpose, might adding one or more subfields to appropriate subject fields be a better fit?
HOME >> MARC Development >> Discussion Paper List
|The Library of Congress >> Especially
for Librarians and Archivists >> Standards
( 12/22/2020 )
|Legal | External Link Disclaimer||Contact Us|