Fix column name for plotting data

[KHwong12]

First thing first, many thanks for releasing these notebooks to the public. I am working on an introductory workshop on spatial analysis with Python and find the materials extremely useful.

Anyway, I ran the cell below and it throws an error.

from mpl_toolkits.axes_grid1 import make_axes_locatable
fig, ax = plt.subplots(1, 1)
divider = make_axes_locatable(ax) #makes it so you can append to the axes

#put another axes to the right of it, at 5% of the total width with 0.1 points of padding in between
cax = divider.append_axes("right", size="5%", pad=0.1) 
# note that you have to specify both ax and cax as arguments for it to work
data.plot(figsize=(10,5), alpha=0.6, column='area', 
          legend=True, ax=ax, cax=cax)

Full Error Message

```
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
/usr/local/lib/python3.7/dist-packages/pandas/core/indexes/base.py in get_loc(self, key, method, tolerance)
   2897             try:
-> 2898                 return self._engine.get_loc(casted_key)
   2899             except KeyError as err:

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()

KeyError: 'area'

The above exception was the direct cause of the following exception:

KeyError                                  Traceback (most recent call last)
5 frames
/usr/local/lib/python3.7/dist-packages/pandas/core/indexes/base.py in get_loc(self, key, method, tolerance)
   2898                 return self._engine.get_loc(casted_key)
   2899             except KeyError as err:
-> 2900                 raise KeyError(key) from err
   2901 
   2902         if tolerance is not None:

KeyError: 'area'
```

What I understand is that this cell aims to symbolise the polygons using their area, which is the same as the previous cell. If that is the case, column='area' is meant to be column='shape_Area'.