title: Quiver plot on a map with python
body: <p>I am trying to plot coloured vectors onto a map in python 2.7.
  I can plot the vectors and their colours with no problem but as soon as I try add the coastline things go wrong. Please help</p>
  
  <pre><code>import matplotlib
  import matplotlib.pyplot as plt
  import numpy as np
  import pandas as pd
  from mpl_toolkits.basemap import Basemap
  
  filename = 'wg_weather1_fixed.csv'
  readcsv = pd.read_csv(filename)
  
  temp = readcsv.Temperature_degC
  wind_speed_kt = readcsv.Wind_Speed_kt
  Wind_Direction = readcsv.Wind_Direction
  lat = readcsv.Latitude
  lon = readcsv.Longitude
  
  
  Wind_speed_2 = wind_speed_kt*1.852
  
  # extract U and V components
  WG_wind_U = Wind_speed_2 * np.sin((360-Wind_Direction)*np.pi/180)
  WG_wind_V = -Wind_speed_2*np.cos((360-Wind_Direction)*np.pi/180)
  
  m = Basemap(projection='merc',llcrnrlat=-32.2,urcrnrlat=-29,\
             llcrnrlon=30,urcrnrlon=33,lat_ts=5,resolution='i')
  
  # Create colour bar
  norm = matplotlib.colors.Normalize()
  norm.autoscale(temp)
  cm = matplotlib.cm.CMRmap
  
  sm = matplotlib.cm.ScalarMappable(cmap=cm, norm=norm)
  sm.set_array([])
  
  # Plot
  q = m.quiver(lon,lat,WG_wind_U,WG_wind_V,color=cm(norm(temp)))
  
  plt.xlabel('Longitude')
  plt.ylabel('Latitude')
  plt.quiverkey(q,0.9, 0.05, 30, r'$30 \frac{Kp}{h}$',labelpos='W',fontproperties={'size': 15,'weight': 'bold'})
  cbar = plt.colorbar(sm)
  
  plt.show()
  </code></pre>
  
  <p>Essentially I need to add a coastline to this plot:
  <a href="https://i.stack.imgur.com/t0SX5.png" rel="nofollow noreferrer">enter image description here</a></p>