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# A quick insight at world population

## Collecting population data

In the below we retrieve population data from the
[World Bank](http://www.worldbank.org/)
using the [wbdata](https://github.com/OliverSherouse/wbdata) python package

```{python}
import pandas as pd
import wbdata as wb

pd.options.display.max_rows = 6
pd.options.display.max_columns = 20
```

Corresponding indicator is found using search method - or, directly,
the World Bank site.

```{python}
wb.search_indicators('Population, total')  # SP.POP.TOTL
# wb.search_indicators('area')
# => https://data.worldbank.org/indicator is easier to use
```

Now we download the population data

```{python}
indicators = {'SP.POP.TOTL': 'Population, total',
              'AG.SRF.TOTL.K2': 'Surface area (sq. km)',
              'AG.LND.TOTL.K2': 'Land area (sq. km)',
              'AG.LND.ARBL.ZS': 'Arable land (% of land area)'}
data = wb.get_dataframe(indicators, convert_date=True).sort_index()
data
```

World is one of the countries

```{python}
data.loc['World']
```

Can we classify over continents?

```{python}
data.loc[(slice(None), '2017-01-01'), :]['Population, total'].dropna(
).sort_values().tail(60).index.get_level_values('country')
```

Extract zones manually (in order of increasing population)

```{python}
zones = ['North America', 'Middle East & North Africa',
         'Latin America & Caribbean', 'Europe & Central Asia',
         'Sub-Saharan Africa', 'South Asia',
         'East Asia & Pacific'][::-1]
```

And extract population information (and check total is right)

```{python}
population = data.loc[zones]['Population, total'].swaplevel().unstack()
population = population[zones]
assert all(data.loc['World']['Population, total'] == population.sum(axis=1))
```

## Stacked area plot with matplotlib

```{python}
import matplotlib.pyplot as plt
```

```{python}
plt.clf()
plt.figure(figsize=(10, 5), dpi=100)
plt.stackplot(population.index, population.values.T / 1e9)
plt.legend(population.columns, loc='upper left')
plt.ylabel('Population count (B)')
plt.show()
```

## Stacked bar plot with plotly

```{python}
import plotly.offline as offline
import plotly.graph_objs as go

offline.init_notebook_mode()
```

```{python}
data = [go.Scatter(x=population.index, y=population[zone], name=zone, stackgroup='World')
        for zone in zones]
fig = go.Figure(data=data,
                layout=go.Layout(title='World population'))
offline.iplot(fig)
```
