NCL_maponly_2.py

This script illustrates the following concepts:

• Outlining continents

• Turning on map country boundaries

• Changing the color of map outlines

• Changing the scale of country boundaries

• Zooming in on a particular area

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

• Original NCL script: https://www.ncl.ucar.edu/Applications/Scripts/maponly_2.ncl

• Original NCL plots: https://www.ncl.ucar.edu/Applications/Images/maponly_2_1_lg.png https://www.ncl.ucar.edu/Applications/Images/maponly_2_2_lg.png https://www.ncl.ucar.edu/Applications/Images/maponly_2_3_lg.png

Import packages

import numpy as np
import cartopy.crs as ccrs
import cartopy.feature as cfeature
import matplotlib.pyplot as plt

import geocat.viz as gv

Plot:

def map_plot(scale, long_min, long_max, lat_min, lat_max, long_labels,
             lat_labels):
    """Plots a map-only figure with continent borders, country borders, and
    lakes at a certain longitude and latitude.

    Parameters
    ----------
    scale : :obj:'str':
        scale of continent borders and lakes

    long_min : :obj:'int':
        minimum longitude for plotting

    long_max : :obj:'int':
        maximum longitude for plotting

    lat_min : :obj:'int':
        minimum latitude for plotting

    lat_max : :obj:'int':
        maximum latitude for plotting

    long_labels : :obj:'list':
        list of tick labels for x axis

    lat_labels : :obj:'list':
        list of tick labels for y axis

    Description
    -----------
        Plots a figure with longitude with range long_min to long_max and latitude with
        range from lat_min to lat_max. The scale of the continent borders and
        lakes depends on the scale variable. The latitude labels are set by lat_labels.
    """

    # Define the projection and generate axes using Cartopy
    projection = ccrs.PlateCarree()
    # Generate figure with (width, height) in inches
    fig = plt.figure(figsize=(7, 7))
    ax = plt.axes(projection=projection)

    # Add in country borders, continent borders, and lakes
    ax.add_feature(
        cfeature.NaturalEarthFeature(category='cultural',
                                     name="admin_0_countries",
                                     scale="110m",
                                     facecolor="none",
                                     edgecolor="black",
                                     linewidth=0.2))
    ax.add_feature(cfeature.LAND.with_scale(scale),
                   edgecolor="#4141a0",
                   facecolor="none")
    ax.add_feature(cfeature.LAKES.with_scale(scale),
                   edgecolor="#4141a0",
                   facecolor="none")

    # Set extent to show particular area of the map
    ax.set_extent((long_min, long_max, lat_min, lat_max), crs=projection)

    # Use geocat.viz.util convenience function to add minor and major tick lines
    gv.add_major_minor_ticks(ax,
                             x_minor_per_major=3,
                             y_minor_per_major=3,
                             labelsize=15)

    # Use geocat.viz.util convenience function to set axes parameters without calling several matplotlib functions
    # Set axes limits, tick values, and tick labels for both latitude and longitude
    gv.set_axes_limits_and_ticks(ax,
                                 xlim=(long_min, long_max),
                                 ylim=(lat_min, lat_max),
                                 xticks=np.linspace(long_min, long_max + 20, 4),
                                 yticks=np.linspace(lat_min, lat_max, 4),
                                 xticklabels=long_labels,
                                 yticklabels=lat_labels)
    # Show plot with minimal whitespace
    plt.tight_layout()
    plt.show()


# Latitude and longitude labels for the top subplot
plt1_long_labels = ["90E", "120E", "150E", ""]
plt1_lat_labels = ["", "30S", "0", "30N"]

# Latitude and longitude labels for the middle and bottom subplots
plt23_long_labels = ["0", "30E", "60E", ""]
plt23_lat_labels = ["", "30N", "60N", "90N"]

# Plot all three subplots
map_plot('110m', 90, 160, -50, 30, plt1_long_labels, plt1_lat_labels)
map_plot('110m', 0, 70, 10, 90, plt23_long_labels, plt23_lat_labels)
map_plot('10m', 0, 70, 10, 90, plt23_long_labels, plt23_lat_labels)

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