Cartopy Tutorial¶

This notebook is intended to be used with the Scripps Institution of Oceanography Software Carpentry Workshop in August of 2025. Tutorial will give a basic overview of Cartopy and many of its plotting features in Earth Sciences using the SWOT dataset

Cartopy is a Python package used for geospatial data processing which can easily produce maps

[70]:

import numpy as np
import xarray as xr
import matplotlib.pyplot as plt
import cartopy.crs as ccrs
import cartopy.feature as cfeature
import pandas as pd
import os

[3]:

# Path to the NetCDF file
data_path = "/Users/tgstone/data/SIO_software_carpentries"
swot_file = "swot_l3_ssh_pass_013.nc"
path = os.path.join(data_path, swot_file)


# Open the dataset using xarray
ds = xr.open_dataset(path)

# Display data
ds

Satellite Data with Mapping¶

For this exercise we will be looking at the Sea Surface Height Anomalies (SSHA) variable in the SWOT track 13 array. To do this we will

extract the varaibles from the dataset
plot the global path
Zoom in on an area along the California coast

[4]:

lons = ds['longitude'].values
lats = ds['latitude'].values
ssha = ds['ssha'].values

[5]:

# Plot Horizontal Geostrophic Velocity (ugos)
plt.figure(figsize=(15, 7))
ax1 = plt.axes(projection=ccrs.PlateCarree())
ax1.set_global()
ax1.coastlines()
cb1 = plt.pcolormesh(lons, lats, ssha, transform=ccrs.PlateCarree())
plt.colorbar(cb1, ax=ax1, orientation='vertical', label='Sea Surface Height Anomaly (m)')
#ax1.set_xticks(np.arange(-180, 181, 30), crs=ccrs.PlateCarree())
#ax1.set_yticks(np.arange(-90, 91, 30), crs=ccrs.PlateCarree())
ax1.gridlines(draw_labels=True, dms=True, x_inline=False, y_inline=False)
plt.title('SWOT Track 13 Global Path - Sea Surface Height Anomaly (ssha)')
plt.xlabel('Longitude')
plt.ylabel('Latitude')

plt.show()

../../_images/in_workshop_python_earth_science_cartopy_6_0.png

[6]:

# Zoom in on a section
plt.figure(figsize=(10, 7))
ax_zoom = plt.axes(projection=ccrs.PlateCarree())
ax_zoom.set_extent([-130, -120, 32, 42], crs=ccrs.PlateCarree())
ax_zoom.coastlines()
cb_zoom = plt.pcolormesh(lons, lats, ssha, transform=ccrs.PlateCarree())
plt.colorbar(cb_zoom, ax=ax_zoom, orientation='vertical', label='Sea Surface Height Anomaly (m)')
ax_zoom.gridlines(draw_labels=True, dms=True, x_inline=False, y_inline=False)
plt.title('SWOT Track 13 - California Coast Zoom: Sea Surface Height Anomaly (ssha)')
plt.xlabel('Longitude')
plt.ylabel('Latitude')
plt.tight_layout()
plt.show()

../../_images/in_workshop_python_earth_science_cartopy_7_0.png