The Reid Isobath Set, Digitized from GEBCO Charts for the Pacific (N&S), Atlantic (N&S), Indian, Arctic and Mediterranean

This data set provides a stream of coordinates describing a specific isobath as
seen in map view. This differs from the usual arrangement that provides depth
at ocean positions and requires intensive contouring. The scheme provides a
simple, economical way to put bathymetric contours on maps of various types and
scales. To facilitate file handling the world is divided into 8 ocean areas,
with the complete set requiring about 6.5 mbytes of storage.

The originators (at Scripps) use the data to prepare working maps for the study
of global ocean circulation. Maps for publication are still prepared by hand
using the working maps as a guide. Typically only one isobath is plotted on a
map; when more are plotted, the isobaths are at 2-3 thousand meter intervals.

Method of preparation:

A. Prepare tracings from each of the 18 GEBCO maps
B. Digitize the tracings on a (balky) digitizing tablet
C. Convert the x-y digitizing coordinates to latitude and longitude
D. Compress the lat-lon positions into an incremental format
E. Combine the maps into 8 ocean areas.

Known Problem Areas:

A. The Pacific around Panama.
B. The area off Argentina where Gebcos 512 and 516 overlap.

Glitches:

We (at Scripps) have plotted all the isobaths dozens of times so we know about
all the mistakes. Displayed adjacent isobaths (eg. 1000 and 1500) will
occasionally overlap. We really did try to make it perfect, but if you could
see what we worked with you would understand why we can live with the mistakes
and why we have little intention of fixing any more.

Structure:

Each ocean area contains one or more of the 5th edition Gebco bathymetry
charts and contains 9-19 separate files, each containing a particular isobath.

North Pacific -- 502,503,506,507
South Pacific -- 510,511,514,515
North Atlantic -- 501,504,508
South Atlantic -- 512,516
Indian -- portion 505,509,513
Mediterranean -- portion 505
Arctic -- 517
Antarctic -- 518

Unpacking the data:

All the data is archived in character form (formatted) and is compressed using
a simple incremental scheme. The expansion scheme can be easily gleaned from
the fortran subroutine included in the distribution. This subroutine (CONBAT)
comes directly from our mapping program 'Lamprey'. Also included is a program
(SUBSET) that can make subsets of a larger file based on an input latitude -
longitude window.