Global topographic dataset at half-degree resolution, downloaded from
a NOAA server on May 18, 2019. Longitude, accessible as
topoWorld[["longitude"]], ranges from -179.75 to 129.75 degrees north.
topoWorld[["latitude"]]) ranges from -89.75 to 89.75 degrees east.
topoWorld[["z"]]) is measured in metres above nominal sea level.
The coarse resolution can be a problem in plotting depth contours along with
coastlines in regions of steep topography. For example, near the southeast
corner of Newfoundland, a 200m contour will overlap a coastline drawn with
coastlineWorldFine from the ocedata package. The solution in such cases is to
download a higher-resolution topography file, perhaps using
download.topo(), and then use
to create another
topo object. (With other data
as.topo() may be helpful.)
This is created with
read.topo(), using a file downloaded with
topoFile <- download.topo(west=-180, east=180, south=-90, north=90, resolution=30, destdir=".")
From late 2009 until May 18, 2019, the
topoWorld dataset was created
with a fairly complicated code that read a binary file downloaded from NOAA
decoded, decimated from 1/12th degree resolution to 1/2 degree resolution, and
matrixShiftLongitude() to put longitude
between -180 and 180 degrees. The new scheme for creating the dataset,
(see “Source”) is much simpler, and also a much better model
of how users are likely to deal with topography files in the more
modern netCDF format. Note that the new version differs from the old one
in longitude and latitude being shifted by 1/4 degree,
and by a mean elevation difference of under 10m. The old and new
versions appear identical when plotted at the global scale that is
the recommended for such a coarse topographic file.