DATE: December 18, 2001
NAME: Encoding Variable Length Coordinate Formats in Field 034 (Coded Cartographic Mathematical Data) in the MARC 21 Bibliographic Format
SOURCE: ALA Map and Geography Round Table; National Imagery and Mapping Agency
SUMMARY: This paper proposes changing field 034 by removing the fixed length nature of subfields $d, $e, $f, and $g. This would allow for recording coordinates using different formats, in particular using decimal degrees.
KEYWORDS: Field 034 (BD); Coded Cartographic Mathematical Data (BD); Coordinates (BD)
12/18/01 - Made available to the MARC 21 community for discussion.
01/21/02 - Results of the MARC Advisory Committee discussion - Approved. Participants recommended that Mary Larsgaard (University of California, Santa Barbara) and David Freeman (NIMA) assist with the revision of the application instructions for field 034 in the MARC 21 documentation.
03/20/02 - Results of LC/NLC review - Agreed with the MARBI decisions.
PROPOSAL NO. 2002-09: Encoding Variable Length Coordinate Formats in Field 034
In early 1994, the Content Standard for Digital Geospatial Data was issued by the U.S. Federal Geospatial Data Committee (FGDC). A Presidential Executive Order directed that effective January 1, 1995 this standard was to be used by all Federal agencies for electronic (and eventually hard-copy) cartographic materials. Since the time frame was very short, the map-cataloging community requested that MARBI approve a number of fields to accommodate the standard, and MARBI did so.
After a few years of working with the new fields, and in recognition that there were other areas within AACR2R for cartographic materials that required updating, an international group the Anglo-American Cataloguing Committee for Cartographic Materials (AACCCM) began work in the late 1990s on rule change proposals. MAGERT took on the task of being the body moving the proposals forward; the proposals were submitted to CC:DA and from thence took the usual rule-revision route. The Joint Steering Committee for the Revision of AACR (JSC) has considered these proposals at various meetings and has essentially completed that work. Changes in AACR2R for cartographic materials are expected to appear in summer of 2002. This proposal considers one of the changes that allows for the encoding of decimal degrees and other variable length coordinate formats in field 034 (Coded Cartographic Mathematical Data). Additional proposals may follow if format changes are necessary, although some of the rule changes may require display changes in local systems or revisions to examples rather than changes to the format itself.
2.1. Current descriptions for recording coordinates in field 034
Field 034 (Coded Cartographic Mathematical Data) contains cartographic mathematical data including scale, projection and/or coordinates in coded form. The following subfields are used for coordinates:
|$d - Coordinates--westernmost longitude (NR)
$e - Coordinates--easternmost longitude (NR)
$f - Coordinates--northernmost latitude (NR)
$g - Coordinates--southernmost latitude (NR)
$s - G-ring latitude (R)
$t - G-ring longitude (R)
According to AACR2 the data is expressed in degrees, minutes and seconds of the sexagesimal system taken from the Greenwich prime meridian. The format specifies that the data in these subfields is eight characters in length and recorded in the form hdddmmss (hemisphere-degrees-minutes-seconds). Note that this restriction is not specified in subfields $s and $t, although they also contain coordinates. It is not clear how these have been implemented.
|034||1#||$aa $b253440 $dE0790000 $eE0860000 $fN0200000 $gN0120000|
2.2. Other coordinate formats.
Other coordinate formats are used by the cartographic community, including decimal degrees, degrees decimal minutes, and NIMA's degrees minutes seconds with seconds expanded to the thousands place.
A proposed rule change from AACR2R allows for one of these alternate formats, coding coordinates as decimal degrees:
|Optionally, record coordinates as decimal degrees. Coordinates given in decimal degrees for locations east of Greenwich and north of the equator are expressed as positive numbers and may be preceded by a plus sign. Locations west of Greenwich and south of the equator are expressed as negative numbers and are preceded by a minus sign. Do not include the plus or minus sign, but precede each coordinate by W, E, N, or S, as appropriate.|
|(W 95.15°W 74.35°/N 56.85°N 41.73°)|
The preference of the computer-science community is that coordinates be given with no letter indications as to longitude or latitude but rather that a minus sign is used for W longitude and S latitude, and a plus sign (or no sign) for E longitude and N latitude. Map catalogers have discovered through experimentation that converting from degrees/minutes/seconds (DMS) to decimal degrees (DD) can require up to six decimal places in order for the conversion to be sufficiently precise. A set of coordinates must either be all in DMS or all in DD; but it is conceivable that a library would need to enter both DMS and DD values for one bounding box or g-ring set of coordinates. Field 034 is already repeatable, so it could be repeated if both forms are given.
2.3. Changes needed for recording variable length coordinate formats.
The easiest and most practical option for accommodating decimal degrees and other variable length coordinate formats in field 034 is to remove the fixed length specification and allow for different forms of coordinates to be recorded. If these subfields were not fixed length at eight characters, decimal degrees could be recorded as well as other variable length formats; a system could determine the format used by the number of characters and/or the presence of the decimal. If both forms need to be recorded, the field would be repeated.
Alternatively, in addition to removing the fixed length specification subfield $2 could be defined to specify the form of the data recorded if it is considered necessary to explicitly indicate the format in which the coordinates are recorded. However, the format is easily recognized by the number of characters and the placement of the decimal point, so the additional subfield seems unnecessary.
Another alternative is to define new subfields to record coordinates expressed
in decimal degrees.
Subfields $u-$x are the only four subfields together that are available. However, the disadvantage to this approach is that it is a more significant change in the format and it defines different subfields for essentially the same data expressed only in a different way. In addition, since various alternative formats are possible, they would have to be defined as coordinates in any format other than that in subfields $d-$g.
2.4. Recording decimal degrees.
For decimal degrees, there are a variety of ways in which the data may be recorded. The more acceptable method for computer software is to use plus and minus signs, with no letters. Example:.
|034 $d -180.0000 $e +180.0000 $f +90.0000 $g -09.0000|
2.5. Degrees/minutes/seconds to thousandths.
The National Imagery and Mapping Agency creates sheet level cataloging records
that require precision in recording coordinates for map production and geospatial
searching. It has encoded coordinates in field 034 subfields using a combination
of letters (W, E, N, S), degrees, minutes and seconds, which are recorded as
decimals to the thousands. The following example is from a National Imagery
and Mapping Agency record:
|034||10||$aa $b10000 $dE1034031.000 $eE1034524.000 $fN0012827.000 $gN0012543.000 $sN0012543.713 $tE1034031.845 $sN0012826.533 $tE1034031.770 $sN0012826.665 $tE103422.999 $sN0012543.844 $tE1034523.068|
2.6. Degrees, decimal minutes.
Degrees, decimal minutes is another coordinate format which uses letters, degrees and minutes recorded as decimals such as: W09224.2 (W92 degrees, 24.2 minutes).
Because of the variation in recording coordinates, subfields $d, $e, $f, and $g need to become variable length subfields. Subfields $s and $t for G-ring coordinates are not currently specified as fixed and should be variable length as well. Adding format flexibility to field 034 should accommodate additional changes to AACR2R.
In field 034 (Coded Cartographic Mathematical Data) of the MARC 21 Bibliographic Format: