diff --git a/django_lostplaces/lostplaces/models.py b/django_lostplaces/lostplaces/models.py
index 049999e..e56e358 100644
--- a/django_lostplaces/lostplaces/models.py
+++ b/django_lostplaces/lostplaces/models.py
@@ -57,7 +57,8 @@ class Taggable(models.Model):
 class Mapable(models.Model):
     '''
     This abstract model class represents an object that can be
-    displayed on a map.
+    displayed on a map. Subclasses have to provide absolute urls,
+    see https://docs.djangoproject.com/en/3.1/ref/models/instances/#get-absolute-url
     '''
     class Meta:
         abstract = True