Impact of double axis in data display

In [2]:

from matplotlib import pyplot as plt
import seaborn as sns
import numpy as np
import pandas as pd

# Aesthetics
sns.set_style('ticks')
plt.rcParams["font.family"] = "serif" # use Serif style as default font

In [8]:

# Import World Bank population data for Austria and China
df = (
    pd.read_csv('../data/API_SP.POP.TOTL_DS2_en_csv_v2_320414/API_SP.POP.TOTL_DS2_en_csv_v2_320414.csv', skiprows=3)
    .drop(columns=['Indicator Code', 'Indicator Name', '2023', 'Unnamed: 68'])
    .melt(id_vars=['Country Name','Country Code'])
    .rename({'Country Name':'country-name', 'Country Code':'country-code', 'variable':'year', 'value': 'population'}, axis=1)
    .assign(year=lambda df_: pd.to_numeric(df_.year))
    .loc[lambda df_: df_['country-name'].isin(['Austria','China'])]
    .reset_index(drop=True)
)

	country-name	country-code	year	population
0	Austria	AUT	1960	7.047539e+06
1	China	CHN	1960	6.670700e+08
2	Austria	AUT	1961	7.086299e+06
3	China	CHN	1961	6.603300e+08
4	Austria	AUT	1962	7.129864e+06
...	...	...	...	...
121	China	CHN	2020	1.411100e+09
122	Austria	AUT	2021	8.955797e+06
123	China	CHN	2021	1.412360e+09
124	Austria	AUT	2022	9.041851e+06
125	China	CHN	2022	1.412175e+09

126 rows × 4 columns

In [47]:

fig= plt.figure(figsize=(10,4))

ax1 = fig.add_subplot(121)
ax2 = fig.add_subplot(122)

ax1.plot(df.loc[df['country-name'] == 'China']['year'], df.loc[df['country-name'] == 'China']['population'], label='China')
ax1.plot(df.loc[df['country-name'] == 'China']['year'], df.loc[df['country-name'] == 'Austria']['population'], label='Austria')
ax1.set(xlabel="Year", ylabel='Population')
ax1.legend()

ax2_twin = ax2.twinx()
ax2.plot(df.loc[df['country-name'] == 'China']['year'], df.loc[df['country-name'] == 'China']['population'], c='tab:blue')
ax2_twin.plot(df.loc[df['country-name'] == 'China']['year'], df.loc[df['country-name'] == 'Austria']['population'], c='tab:orange')
ax2.set_xlabel("Year")
ax2.set_ylabel('Population China', color='tab:blue')
ax2_twin.set_ylabel('Population Austria', rotation=-90, va='bottom', color='tab:orange')

ax1.set_title('Same Y-axis')
ax2.set_title('Double Y-axis')
fig.savefig('../figures/double-axis.pdf', bbox_inches='tight')
plt.show()

Figure 1: Visual effect of using double Y-axis on data of different scales.

Figure 1: Visual effect of using double Y-axis on data of different scales.