old_contents: from django.contrib.gis.db import models
  from django_hstore import hstore
  
  
  class Measurement(models.Model):
      """A measurement at a point in space/time."""
      created_timestamp = models.DateTimeField(auto_now_add=True)
      reference_timestamp = models.DateTimeField(null=True, blank=True)
      location = models.PointField()
      location_reference = models.CharField(
          max_length=200, null=True, blank=True,
          help_text="A friendly/reference name for this site")
      observations = hstore.DictionaryField()
  
      observer = models.EmailField(
          null=True, blank=True,
          help_text="If a Citizen Scientist added this data - their email.")
      source = models.ForeignKey(
          'supplements.DataSource', null=True, blank=True,
          help_text="If this data came from an historic source, what is it?"
      )
  
      objects = models.GeoManager()
      observations_manager = hstore.HStoreManager()
  
      def __unicode__(self):
          return u"Observation at {0}".format(self.created_timestamp)
  
new_contents: from django.contrib.gis.db import models
  from django_hstore import hstore
  
  
  class Measurement(models.Model):
      """A measurement at a point in space/time."""
      created_timestamp = models.DateTimeField(auto_now_add=True)
      reference_timestamp = models.DateTimeField(null=True, blank=True)
      location = models.PointField()
      location_reference = models.CharField(
          max_length=200, null=True, blank=True,
          help_text="A friendly/reference name for this site")
      observations = hstore.DictionaryField()
  
      observer = models.EmailField(
          null=True, blank=True,
          help_text="If a Citizen Scientist added this data - their email.")
      source = models.ForeignKey(
          'supplements.DataSource', null=True, blank=True,
          help_text="If this data came from an historic source, what is it?"
      )
  
      objects = models.GeoManager()
      observations_manager = hstore.HStoreManager()
  
      class Meta:
          ordering = ('-reference_timestamp',)
  
      def __unicode__(self):
          return u"Observation at {0}".format(self.created_timestamp)
  
subject: set default ordering of observations based on date