In NCL version 4.2.0.a23, some built in tickmarks have been added to the language. To get these tickmarks, you need to set pmTickMarkDisplayMode = "Always". Not all of the tick mark resources are available for maps.
Map Tickmarks
Two plot templates categories (cylindrical
equidistant and polar stereographic
projections) come with "nice" lat/lon labels. These have been manually
added by the developers.
mptick_2.ncl: Turns on the
tickmarks available in NCL version 4.2.0.a23 and later.
pmTickMarkDisplayMode = "Always" will turn on these tickmarks.
The built-in tickmarks contain a degree symbol.
mptick_3.ncl: Demonstrates what
happens to the built-in tickmarks when you zoom in to less than one
degree.
mptick_4.ncl: Demonstrates how to
adjust the tickmark spacing. This only works for the default tickmarks
(see example 1)
gsnMajorLatSpacing, gsnMinorLatSpacing, gsnMajorLonSpacing, gsnMinorLonSpacing, can be used to adjust the spacing of the default tickmarks on a ce map projection.
tmXBMinorOn, tmXTMinorOn, tmYLMinorOn, tmYRMinorOn, can be used to turn off the minor tickmarks on a particular side of a map projection.
mptick_5.ncl: Demonstrates how to
change the tickmark label font height, adjust the tickmark length,
and turn on grid lines (a map resource). This works for both the
default and built-in tickmarks.
tmXBLabelFontHeightF and its relatives (XT,YL etc) adjust the font height of tickmark labels.
tmXBMajorLengthF and adjusts the tickmark length. The plot template is designed such that changing one tickmark length (e.g. XB), changes them all.
mpGridAndLimbOn turns on the grid lines. This is a function of the map and not tickmarks. Note that there are numerous other mpGrid* resources that control its spacing and appearance.
mptick_6.ncl: Demonstrates
how to change the default "0" to a "EQ"
To do this change, you must explicitly define the tickmarks and their
labels using:
tmXBMode =
"Explicit"
tmXBValues =
(/.../)
tmXBLabels = (/.../)
mptick_7.ncl: Demonstrates
how to get a degree symbol in the map tickmark labels, and how to
turn on labels for the top and right axes.
You must first explicitly define the tickmarks and their labels as defined in example 6 above, and then use text function codes to get a degree symbol. Set tmXTLabelsOn and tmYRLabelsOn to True to get tickmark labels on the top and right axes. Note that setting pmTickMarkDisplayMode = "Always" will also have the effect of giving you map tickmark labels with degree symbols (see example 2).