NCL_coast_1.py

This script illustrates the following concepts:

• Drawing color-filled contours over a cylindrical equidistant map

• Specifying and drawing three different resolutions for map outlines

• Zooming in on a particular area on the map

• Moving title and colorbar locations

• Following best practices when choosing a colormap. More information on colormap best practices can be found here.

See following URLs to see the reproduced NCL plot & script:

• Original NCL script: https://www.ncl.ucar.edu/Applications/Scripts/coast_1.ncl

• Original NCL plot: https://www.ncl.ucar.edu/Applications/Images/coast_1_1_lg.png https://www.ncl.ucar.edu/Applications/Images/coast_1_2_lg.png https://www.ncl.ucar.edu/Applications/Images/coast_1_3_lg.png

Import packages

import numpy as np
import xarray as xr
import cartopy.crs as ccrs
import cartopy.feature as cfeature
from cartopy.mpl.gridliner import LongitudeFormatter, LatitudeFormatter
import matplotlib.pyplot as plt

import geocat.datafiles as gdf
import geocat.viz as gv

Read in data:

# Open the netCDF data file using xarray
ds = xr.open_dataset(gdf.get("netcdf_files/tpom000.partial.nc"))

# Extract a slice of the data
t = ds.t

Plot:

def Plot(res, title):

    fig = plt.figure(figsize=(8, 6))

    # Generate axes, using Cartopy, drawing coastlines, and adding features
    fig.tight_layout(pad=3)
    projection = ccrs.PlateCarree()
    ax1 = plt.axes(projection=projection)
    ax1.coastlines(resolution=res, linewidths=0.5)
    ax1.add_feature(cfeature.LAND.with_scale(res), facecolor="wheat")

    # Contourf-plot data
    temp = t.plot.contourf(ax=ax1,
                           transform=projection,
                           levels=25,
                           vmin=14.9,
                           vmax=17.3,
                           cmap='magma',
                           add_colorbar=False)

    # Add color bar
    cbar_ticks = np.arange(15, 17.3, 0.3)
    cbar = plt.colorbar(temp,
                        orientation='horizontal',
                        shrink=0.8,
                        pad=0.073,
                        extendrect=True,
                        ticks=cbar_ticks)

    cbar.ax.tick_params(labelsize=10)

    # Use geocat.viz.util convenience function to set axes limit and tick values
    gv.set_axes_limits_and_ticks(ax1,
                                 xlim=(-8, -3),
                                 ylim=(35, 37),
                                 xticks=np.linspace(-3, -8, 6),
                                 yticks=np.linspace(35, 37, 3))

    # Use geocat.viz.util convenience function to add major tick lines
    gv.add_major_minor_ticks(ax1, y_minor_per_major=1, labelsize=12)

    # Use geocat.viz.util convenience function to add lat and lon tick labels
    gv.add_lat_lon_ticklabels(ax1)

    # Remove degree symbol from tick label
    ax1.yaxis.set_major_formatter(LatitudeFormatter(degree_symbol=''))
    ax1.xaxis.set_major_formatter(LongitudeFormatter(degree_symbol=''))

    # Use geocat.viz.util convenience function to set titles and labels
    gv.set_titles_and_labels(ax1,
                             righttitle="Deg C",
                             righttitlefontsize=15,
                             lefttitle="Temperature",
                             lefttitlefontsize=15,
                             xlabel="",
                             ylabel="")

    plt.suptitle("Strait of Gibraltar", x=.5, y=.83, fontsize=18)
    plt.title(title, x=.5, y=1.07, fontsize=15)
    plt.tight_layout()
    plt.show()


# Plot maps
Plot('110m', "Low Res Coastline")
Plot('50m', "Medium Res Coastline")
Plot('10m', "High Res Coastline (default)")

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