"KeyError: 0" when calculating area of polygon using GeoPandas

Question

I am working in Jupyter Notebook and overlaying two GeoJSON files. One is property, the other is council zones.

I am selecting the property id's and then clipping the zones that lie within the extent

 ITT_PROP_select = ITT_PROP.query("(PROPID == 40932672)")
 ITT_PROP_select

 select = gpd.clip(ITT_Zone, ITT_PROP_select)
 select 

However when using the code below, I am unable to add a new column and calculate the areas for each row.

from shapely.geometry import shape
for i in range(len(select)):
    select.loc[i, 'area_m2'] = shape(select.loc[i,'geometry']).area

The code returns:

KeyError: 0

Answer 1

The usual way to calculate area and store it as a new column (attribute) is:

df["area"] = df.area

but you might see a useful warning:

UserWarning: Geometry is in a geographic CRS. Results from 'area' are likely incorrect. Use GeoSeries.to_crs() to re-project geometries to a projected CRS before this operation.

You can also use geometry_area_perimeter from PyProj >= 2.3.0 to calculate the area in m²:

import geopandas
df = geopandas.read_file("file.shp")
geod = df.crs.get_geod()
df["area_m2"] = df.geometry.apply(lambda g: abs(geod.geometry_area_perimeter(g)[0]))