28 of 100: Nested half circles chart in matplotlib
At the beginning of the year I challenged myself to create all 100 visualizations using python and matplotlib from the 1 dataset,100 visualizations project and I am sharing with you the code for all the visualizations.
Note: Data Viz Project is copyright Ferdio and available under a Creative Commons Attribution – Non Commercial – No Derivatives 4.0 International license. I asked Ferdio and they told me they used a Design tool to create all the plots.
Collaborate
There are a ton of improvements that can be made on the code, so let me know in the comments any improvements you make and I will update the post accordingly!
To be improved: A lot of hardcoding of the positions and labels, need to review.
This is the original viz that we are trying to recreate in matplotlib:

Import the packages
We will need the following packages:
import matplotlib.pyplot as plt
from matplotlib.patches import Wedge
from matplotlib.lines import Line2D
from matplotlib.markers import MarkerStyle
import pandas as pd
import numpy as np
Generate the data
We could actually go from numpy to matplotlib, but most data projects use pandas to transform the data, so I am using a pandas dataframe as the starting point.
color_dict = {"Norway": "#2B314D", "Denmark": "#A54836", "Sweden": "#5375D4", }
xy_ticklabel_color, grand_totals_color, grid_color, datalabels_color ='#757C85',"#101628", "#C8C9C9", "#FFFFFF"
data = {
"year": [2004, 2022, 2004, 2022, 2004, 2022],
"countries" : [ "Denmark", "Denmark", "Norway", "Norway","Sweden", "Sweden",],
"sites": [4,10,5,8,13,15]
}
df= pd.DataFrame(data)
index | year | countries | sites |
---|---|---|---|
0 | 2004 | Sweden | 13 |
1 | 2022 | Sweden | 15 |
2 | 2004 | Denmark | 4 |
3 | 2022 | Denmark | 10 |
4 | 2004 | Norway | 5 |
5 | 2022 | Norway | 8 |
We need to create the subtotals for each year, the percentage change and then sort the data.
df['sub_total'] = df.groupby('countries')['sites'].transform('sum')
df['pct_change'] = df.groupby('countries', sort=False)['sites'].apply(
lambda x: x.pct_change()).to_numpy()*-1
df = df.sort_values(['year','sites' ], ascending=True ).reset_index(drop=True)
#map the colors of a dict to a dataframe
df['color']= df.countries.map(color_dict)
index | year | countries | sites | sub_total | pct_change | color |
---|---|---|---|---|---|---|
0 | 2004 | Denmark | 4 | 14 | NaN | #A54836 |
1 | 2004 | Norway | 5 | 13 | NaN | #2B314D |
2 | 2004 | Sweden | 13 | 28 | NaN | #5375D4 |
3 | 2022 | Norway | 8 | 13 | -0.600000 | #2B314D |
4 | 2022 | Denmark | 10 | 14 | -1.500000 | #A54836 |
5 | 2022 | Sweden | 15 | 28 | -0.153846 | #5375D4 |
Define the variables
sites =df.sites.to_numpy()
colors = df.color
theta1, theta2 = 0, 180
radius = (sites/2)
radius[3:] *= -1
centers = [(sites[i]/2,0) for i in range(6)]
label_x = df.groupby(['year','sites'])['sites'].agg(sum).to_list()
label_y = np.repeat([0.2, 0.4],len(df.countries.unique()))
label_y[3:] *= -1
Plot the chart
fig, ax = plt.subplots( figsize=(10,5), facecolor = "#FFFFFF")
ax.set_aspect('equal')
for radie, lb_y,lb_x, site, color, center in zip(radius, label_y, label_x, df.sites, reversed(colors), centers):
patches = Wedge(center, radie, theta1, theta2, color=color,)
ax.add_patch(patches)
ax.annotate(lb_x, xy=(lb_x-0.6, lb_y ), fontsize=8, color = "w",)
ax.text(-4, 1, df.year.min(), color=xy_ticklabel_color, size=12 )
ax.text(-4, -2, df.year.max(), color=xy_ticklabel_color, size=12 )
ax.axhline(y=0,xmin=-4,xmax=17, color =grid_color,lw=0.5,snap=False)
ax.set_xlim([-4, 17])
ax.set_ylim([-8, 8])
#add legend
lines = [Line2D([0], [0], color=c, marker=MarkerStyle('o', fillstyle='top'), mec="w", linestyle='', markersize=20,) for c in colors]
labels = df.countries.unique().tolist()
plt.legend(lines, labels, labelcolor= xy_ticklabel_color,
bbox_to_anchor=(0.5, -0.3), loc="lower center",
ncols = 3,frameon=False, fontsize= 10)
ax.set_xticklabels([])
ax.set_yticklabels([])
ax.set_frame_on(False)
ax.tick_params(axis='both', which='both',length = 0)
The result:

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