[Answered ]-RemovedInDjango110Warning: SubfieldBase has been deprecated

The problem is in this line:

class GeopositionField(with_metaclass(models.SubfieldBase, models.Field)):

Change it to:

class GeopositionField(models.Field):

You’ll also have to implement from_db_value() as described here:
https://docs.djangoproject.com/en/1.9/howto/custom-model-fields/#converting-values-to-python-objects