Python Matplotlib add Colorbar

Question

i've got a problem using MatlobLib with "Custom" Shapes from a shapereader. Importing and viewing inserted faces works fine, but i'm not able to place a colorbar on my figure.

I already tried several ways from the tutorial, but im quite sure there is a smart solution for this problem.

maybe somebody can help me, my current code is attached below:

from formencode.national import pycountry
import itertools
from matplotlib import cm, pyplot
from matplotlib import 
from mpl_toolkits.basemap import Basemap
from numpy.dual import norm
import cartopy.crs as ccrs
import cartopy.io.shapereader as shpreader
import matplotlib as mpl
import matplotlib.colors as colors
import matplotlib.mlab as mlab
import matplotlib.pyplot as plt
import numpy as np

def draw_map_for_non_normalized_data_with_alpha2_counrty_description(data, title=None):

m = Basemap()
ax = plt.axes(projection=ccrs.PlateCarree())

list = []
sum = 0
for key in data:
    sum += data[key]

for key in data.keys():
    new_val = (data[key]+0.00)/sum
    list.append(new_val)
    data[key] = new_val

#===========================================================================
# print str(min(list))
# print str(max(list))
#===========================================================================

cmap = mpl.cm.cool
colors = matplotlib.colors.Normalize(min(list)+0.0, max(list)+0.0)

labels = []
features = []
for country in shpreader.Reader(shapename).records():
    a3_code = country.attributes["gu_a3"]
    try :
        a2_code =  pycountry.countries.get(alpha3=a3_code).alpha2
    except:
        a2_code = ""

    if a2_code in data:
        val = data[a2_code]

        color = cm.jet(norm(val))

        print str(val) + " value for color: " + str(color)

        labels.append(country.attributes['name_long'])
        feat = ax.add_geometries(country.geometry, ccrs.PlateCarree(), facecolor=color, label=country.attributes['name_long'])

        features.append(feat)   
#ax.legend(features, labels, loc='upper right')
#===========================================================================
# fig = pyplot.figure(figsize=(8,3))    
# ax1 = fig.add_axes([0.05, 0.80, 0.9, 0.15])
#===========================================================================

#cbar = m.colorbar(location='bottom')
cb1 = mpl.colorbar.ColorbarBase(ax, cmap=cmap,norm=colors,orientation='horizontal')
cb1.set_label('foo')

m.drawcoastlines()
m.drawcountries()
if title:
    plt.title(title)

plt.show()

as you can see inside the code, i already tried several ways, but none of them worked for me.

maybe somebody has "the" hint for me.

thanks for help,

kind regards

Your code is very vague to me, it not a complete example. What modules are you using? It looks like you are mixing `Basemap` and `Cartopy` together, that seems already a bit tricky to start with. If you do, it might help to tag your post accordingly. — Rutger Kassies, Aug 26 '14 at 12:51
thanks for your comment, i added the the imports (sorry, they are a bit messed up :( ) - yes, its Cartopy and Basemap, because i've done it according to this "tutorial": http://stackoverflow.com/questions/13397022/fill-countries-in-python-basemap , is there another way to do this easier? — user3066027, Aug 26 '14 at 13:11

Rutger Kassies · Answer 1 · 2014-08-26T14:10:08.460

As mentioned in the comments above, i would think twice about mixing Basemap and Cartopy, is there a specific reason to do so? Both are basically doing the same thing, extending Matplotlib with geographical plotting capabilities. Both are valid to use, they both have their pro's and con's.

In your example you have a Basemap axes m, a Cartopy axes ax and you are using the Pylab interface by using plt. which operates on the currently active axes. Perhaps it theoretically possible, but it seems prone to errors to me.

I cant modify your example to make it work, since the data is missing and your code is not valid Python, the indentation for the function is incorrect for example. But here is a Cartopy-only example showing how you can plot a Shapefile and use the same cmap/norm combination to add a colorbar to the axes.

One difference with your code is that you provide the axes containing the map to the ColorbarBase function, this should be a seperate axes specifically for the colorbar.

import cartopy.crs as ccrs
import matplotlib.pyplot as plt
import matplotlib as mpl
import cartopy.io.shapereader as shpreader

fig, ax = plt.subplots(figsize=(12,6), 
                       subplot_kw={'projection': ccrs.PlateCarree()})

norm = mpl.colors.Normalize(vmin=0, vmax=1000000)
cmap = plt.cm.RdYlBu_r

for n, country in enumerate(shpreader.Reader(r'D:\ne_50m_admin_0_countries_lakes.shp').records()):

    ax.add_geometries(country.geometry, ccrs.PlateCarree(),
                      facecolor=cmap(norm(country.attributes['gdp_md_est'])),
                      label=country.attributes['name'])

ax.set_title('gdp_md_est')

cax = fig.add_axes([0.95, 0.2, 0.02, 0.6])
cb = mpl.colorbar.ColorbarBase(cax, cmap=cmap, norm=norm, spacing='proportional')
cb.set_label('gdp_md_est')

enter image description here

thanks a lot.. hmm the code might be mixed up during copy & paste. thanks for your example! as it works it is fine for me, i'm just looking for a simple way to do it and found just the way above described. i'll try it tonight :) — user3066027, Aug 26 '14 at 15:26
How do you move the colorbar closer to the plot? Mine is too far off. — FaCoffee, May 16 '17 at 14:39

Python Matplotlib add Colorbar

1 Answers1