Note
Click here to download the full example code
NCL_mask_2.py¶
- This script illustrates the following concepts:
Using keyword zorder to mask areas in a plot
Drawing filled land areas on top of a contour plot
Selecting a different colormap to abide by best practices. See the color examples for more information.
- See following URLs to see the reproduced NCL plot & script:
Original NCL script: https://www.ncl.ucar.edu/Applications/Scripts/mask_2.ncl
Original NCL plot: https://www.ncl.ucar.edu/Applications/Images/mask_2_lg.png
- Using zorder:
The
zorder
keyword is used bymatplotlib
to layer elements in a plot. Elements with lowerzorder
values are plotted first and other elements are layered on top based on increasingzorder
values. For more information, please refer tomatplotlib
’s zorder demo page.
Import packages:
import cartopy.crs as ccrs
import cartopy.feature as cfeature
from cartopy.mpl.gridliner import LongitudeFormatter, LatitudeFormatter
import matplotlib.pyplot as plt
import numpy as np
import xarray as xr
import geocat.datafiles as gdf
from geocat.viz import util as gvutil
Read in data:
# Open a netCDF data file using xarray and load the data into xarrays
# Disable time decoding due to missing necessary metadata
ds = xr.open_dataset(gdf.get("netcdf_files/atmos.nc"), decode_times=False)
# Extract a slice of the data at first time step
ds = ds.isel(time=0).drop("time")
TS = ds.TS
# Fix the artifact of not-shown-data around 0 and 360-degree longitudes
TS = gvutil.xr_add_cyclic_longitudes(TS, "lon")
Plot:
# Generate figure (set its size (width, height) in inches)
fig = plt.figure(figsize=(10, 6))
# Generate axes using Cartopy and draw land masses, coastlines, and lakes
ax = plt.axes(projection=ccrs.PlateCarree())
ax.add_feature(cfeature.LAND, facecolor='lightgray', zorder=1)
ax.add_feature(cfeature.COASTLINE, linewidth=0.5, zorder=1)
ax.add_feature(cfeature.LAKES,
linewidth=0.5,
edgecolor='black',
facecolor='None',
zorder=1)
# Plot filled contour
contour = TS.plot.contourf(ax=ax,
transform=ccrs.PlateCarree(),
cmap='magma',
levels=np.arange(216, 315, 3),
extend='neither',
add_colorbar=False,
add_labels=False,
zorder=0)
plt.colorbar(contour,
ax=ax,
ticks=np.linspace(219, 303, 8),
orientation='horizontal',
pad=0.075,
drawedges=True,
shrink=0.7)
# Use geocat.viz.util convenience function to set axes limits & tick values
gvutil.set_axes_limits_and_ticks(ax,
xlim=(-180, 180),
ylim=(-90, 90),
xticks=np.linspace(-180, 180, 13),
yticks=np.linspace(-90, 90, 7))
# Use geocat.viz.util convenience function to add minor and major tick lines
gvutil.add_major_minor_ticks(ax, labelsize=12)
# Use geocat.viz.util convenience function to make latitude and
# longitude tick labels
gvutil.add_lat_lon_ticklabels(ax)
# Remove the degree symbol from tick labels
ax.yaxis.set_major_formatter(LatitudeFormatter(degree_symbol=''))
ax.xaxis.set_major_formatter(LongitudeFormatter(degree_symbol=''))
# Use geocat.viz.util convenience function to add titles
gvutil.set_titles_and_labels(ax,
maintitle='Draw land ON TOP of contours',
lefttitle=TS.long_name,
righttitle=TS.units,
lefttitlefontsize=14,
righttitlefontsize=14)
plt.show()
Total running time of the script: ( 0 minutes 1.137 seconds)