Get Started

Calculating the centroid

The bounding box can range from a city block to a whole state or even country. For simplicity's sake, one way we can deal with handling these data is by translating the bounding box into what's called a centroid, or the center of the bounding box. The calculation of the centroid is straight forward -- we calculate the midpoints of the lines created by the latitude and longitudes.

numpy has been imported as np.

This is a part of the course

“Analyzing Social Media Data in Python”

View Course

Exercise instructions

  • Obtain the first set of coordinates from the place JSON.
  • Calculate the central longitude by adding up the longitude list and dividing by two.
  • Do the same for the latitudes.
  • Apply the calculateCentroid() function to the place column.

Hands-on interactive exercise

Have a go at this exercise by completing this sample code.

def calculateCentroid(place):
    """ Calculates the centroid from a bounding box."""
    # Obtain the coordinates from the bounding box.
    coordinates = place[____][____][0]
        
    longs = np.unique( [x[0] for x in coordinates] )
    lats  = np.unique( [x[1] for x in coordinates] )

    if len(longs) == 1 and len(lats) == 1:
        # return a single coordinate
        return (longs[0], lats[0])
    elif len(longs) == 2 and len(lats) == 2:
        # If we have two longs and lats, we have a box.
        central_long = ____.____(____) / ____
        central_lat  = ____.____(____) / ____
    else:
        raise ValueError("Non-rectangular polygon not supported: %s" % 
            ",".join(map(lambda x: str(x), coordinates)) )

    return (central_long, central_lat)
    
# Calculate the centroids of place     
centroids = tweets_sotu[____].apply(____)
Edit and Run Code