def haversine(lon1, lat1, lon2, lat2):
    """
    Calculate the great circle distance between two points
    on earth (specified in decimal degrees)
    """
    # convert decimal degrees to radians
    lat1 = radians(lat1)
    lon1 = radians(lon1)
    lat2 = radians(lat2)
    lon2 = radians(lon2)
    # haversine formula
    dlon = lon2 - lon1
    dlat = lat2 - lat1
    a = sin(dlat/2)**2 + cos(lat1) * cos(lat2) * sin(dlon/2)**2
    c = 2 * asin(sqrt(a))
    r = 6371 # Radius of earth in kilometers. Use 3956 for miles
    distance_btwn_points= c * r
    return distance_btwn_points

radius = 2.00 # in kilometer
ship_navigation_port=ship_navigation.copy()
ship_navigation_port['port_id']= 0
for port in ports_location['port_id']:
    for index, row in ship_navigation_port.iterrows():
        ship_navigation_port['port_id']= np.where(haversine( ports_location['lon'][port], ports_location['lat'][port], row['lon'], row['lat'])<= radius, ports_location['port_id'][port], 0)