Easy way to find the centroid of a bunch of placemarks from a KML file.

centroidfinder.py

from xml.dom.minidom import parseString

def findCentroidGivenKML(location):
    #Read KML file as a string
    file = open(location)
    data = file.read()
    file.close()

    #Parse that string into a DOM
    dom = parseString(data)

    #initialize latitude and longitude lists
    latitudes = []
    longitudes = []

    #Iterate through a collection of coordinates elements
    for d in dom.getElementsByTagName('coordinates'):
        #Break them up into latitude and longitude
        coords = d.firstChild.data.split(',')
        longitudes.append(float(coords[0]))
        latitudes.append(float(coords[1]))

    #find the centroid
    centerLatitude = sum(latitudes)/len(latitudes)
    centerLongitude = sum(longitudes)/len(longitudes)
    return ([centerLongitude,centerLatitude])