This is a sample extended content type for Plone that uses the Event Schema adding some new fields (Image, Categories and Location). Categories field is using a NamedVocabulariy and Location field uses a TTGoogleMapMarker

imageevent.py

"""Definition of the imageevent content type
"""

from zope.interface import implements

from Products.Archetypes import atapi
from Products.ATContentTypes.content import base
from Products.ATContentTypes.content import schemata

# -*- Message Factory Imported Here -*-
from Products.ATReferenceBrowserWidget.ATReferenceBrowserWidget import *
from Products.ATReferenceBrowserWidget import ATReferenceBrowserWidget

from cambrils.contenttypes.interfaces import Iesdeveniment
from cambrils.contenttypes.config import PROJECTNAME
from cambrils.contenttypes import contenttypesMessageFactory as _

from Products.ATVocabularyManager import NamedVocabulary

from Products.ATContentTypes.content import event
from Products.ATContentTypes.content.event import ATEvent
from Products.ATContentTypes.content.event import ATEventSchema
from Products.ATContentTypes.interfaces import IATEvent

from Products.ATContentTypes.interface.interfaces import ICalendarSupport
from Products.ATContentTypes.lib import calendarsupport as cs
from Products.ATContentTypes.lib.calendarsupport import CalendarSupportMixin
from Products.ATContentTypes.lib.historyaware import HistoryAwareMixin

imageeventSchema = event.ATEventSchema.copy() + atapi.Schema((

    # -*- Your Archetypes field definitions here ... -*-
    atapi.ImageField(
        'Image',
        storage=atapi.AnnotationStorage(),
        widget=atapi.ImageWidget(
            label=_(u"Related image"),
            description=_(u"Select the main news item image."),
        ),
        required=False,
        sizes={'mini': (86, 61), 'normal': (160, 120), 'medium': (290, 144), 'big': (640, 210)},
    ),

    atapi.StringField(
        'Categories',
        widget=atapi.SelectionWidget(
            label="Categories",
        ),
        vocabulary=NamedVocabulary("""agenda""")
    ),

    atapi.ReferenceField(
        'Location',
        widget=ReferenceBrowserWidget(
            label="Location",
        ),
        relationship='MapMarker',
        allowed_types=("TTGoogleMapMarker"),
        multiValued=True,
    ),

))

# Set storage on fields copied from ATContentTypeSchema, making sure
# they work well with the python bridge properties.

imageeventSchema['title'].storage = atapi.AnnotationStorage()
imageeventSchema['description'].storage = atapi.AnnotationStorage()

schemata.finalizeATCTSchema(imageeventSchema, moveDiscussion=False)


class imageevent(base.ATCTContent, CalendarSupportMixin, HistoryAwareMixin):
    """Extended event type with images"""
    implements(Iimageevent)

    meta_type = "imageevent"
    schema = imageeventSchema

    title = atapi.ATFieldProperty('title')
    description = atapi.ATFieldProperty('description')

    # -*- Your ATSchema to Python Property Bridges Here ... -*-
    Imatge = atapi.ATFieldProperty('Imatge')

atapi.registerType(imageevent, PROJECTNAME)