numpy-based method for calculating (great circle) distance between two series of points.

numpy-ified-great-circle.py

import numpy as np
import pandas as pd
from geopy.distance import EARTH_RADIUS
def numpy_distance(src_lats, src_longs, dest_lats, dest_longs):
  """Calculate distance between (effectively) two Series of points."""
    # Convert from degrees to radians.
    src_lats = src_lats.apply(np.deg2rad)
    src_longs = src_longs.apply(np.deg2rad)
    dest_lats = dest_lats.apply(np.deg2rad)
    dest_longs = dest_longs.apply(np.deg2rad)

    # grab sines
    src_lat_sin = src_lats.apply(np.sin)
    dest_lat_sin = dest_lats.apply(np.sin)
    # grab cosines
    src_lat_cos = src_lats.apply(np.cos)
    dest_lat_cos = src_lats.apply(np.cos)

    lng_deltas = dest_longs.subtract(src_longs)
    lng_delta_cos = lng_deltas.apply(np.cos)
    lng_delta_sin = lng_deltas.apply(np.sin)

    return EARTH_RADIUS * np.arctan2(
        np.sqrt(
            (dest_lat_cos * lng_delta_sin) ** 2 +
            (src_lat_cos * dest_lat_sin - src_lat_sin * dest_lat_cos * lng_delta_cos) ** 2
        ),
        src_lat_sin * dest_lat_sin + src_lat_cos * dest_lat_cos * lng_delta_cos
    )

# NOTE: parcel_info is a dataframe I read in from some 100MB+ CSV file. Hooray public data projects!
num_rows = parcel_info.shape[0]
numpy_distance(
    parcel_info['Latitude'],
    parcel_info['Longitude'],
    pd.Series(np.repeat(42.420167, num_rows)),
    pd.Series(np.repeat(-82.968060, num_rows))
)

I believe you have a typo in you function on line 17