diff --git a/src/c3nav/mapdata/__init__.py b/src/c3nav/mapdata/__init__.py
index e69de29b..e69931c9 100644
--- a/src/c3nav/mapdata/__init__.py
+++ b/src/c3nav/mapdata/__init__.py
@@ -0,0 +1,3 @@
+
+
+default_app_config = 'c3nav.mapdata.apps.MapdataConfig'
diff --git a/src/c3nav/mapdata/apps.py b/src/c3nav/mapdata/apps.py
new file mode 100644
index 00000000..e9400555
--- /dev/null
+++ b/src/c3nav/mapdata/apps.py
@@ -0,0 +1,9 @@
+from django.apps import AppConfig
+
+
+class MapdataConfig(AppConfig):
+    name = 'c3nav.mapdata'
+
+    def ready(self):
+        from c3nav.mapdata.render.cache import register_signals
+        register_signals()
diff --git a/src/c3nav/mapdata/models/geometry/base.py b/src/c3nav/mapdata/models/geometry/base.py
index 9d5dc950..501f56cb 100644
--- a/src/c3nav/mapdata/models/geometry/base.py
+++ b/src/c3nav/mapdata/models/geometry/base.py
@@ -28,6 +28,10 @@ class GeometryMixin(SerializableMixin):
         abstract = True
         base_manager_name = 'objects'
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.orig_geometry = None if 'geometry' in self.get_deferred_fields() else self.geometry
+
     def get_geojson_properties(self, *args, **kwargs) -> dict:
         result = OrderedDict((
             ('type', self.__class__.__name__.lower()),
@@ -76,6 +80,14 @@ class GeometryMixin(SerializableMixin):
     def recalculate_bounds(self):
         self.minx, self.miny, self.maxx, self.maxy = self.geometry.bounds
 
+    @property
+    def geometry_changed(self):
+        return self.orig_geometry is None or (self.geometry is not self.orig_geometry and
+                                              not self.geometry.almost_equals(self.orig_geometry, 2))
+
+    def get_changed_geometry(self):
+        return self.geometry if self.orig_geometry is None else self.geometry.symmetric_difference(self.orig_geometry)
+
     def save(self, *args, **kwargs):
         self.recalculate_bounds()
         super().save(*args, **kwargs)
diff --git a/src/c3nav/mapdata/models/geometry/level.py b/src/c3nav/mapdata/models/geometry/level.py
index 12df8292..ae632a55 100644
--- a/src/c3nav/mapdata/models/geometry/level.py
+++ b/src/c3nav/mapdata/models/geometry/level.py
@@ -15,6 +15,7 @@ from c3nav.mapdata.models import Level
 from c3nav.mapdata.models.access import AccessRestrictionMixin
 from c3nav.mapdata.models.geometry.base import GeometryMixin
 from c3nav.mapdata.models.locations import SpecificLocation
+from c3nav.mapdata.render.cache import changed_geometries
 from c3nav.mapdata.utils.geometry import assert_multilinestring, assert_multipolygon, clean_geometry
 
 
@@ -41,6 +42,17 @@ class LevelGeometryMixin(GeometryMixin):
             result['level'] = self.level_id
         return result
 
+    def register_change(self, force=False):
+        if force or self.geometry_changed:
+            changed_geometries.register(self.level_id, self.geometry if force else self.get_changed_geometry())
+
+    def register_delete(self):
+        changed_geometries.register(self.level_id, self.geometry)
+
+    def save(self, *args, **kwargs):
+        self.register_change()
+        super().save(*args, **kwargs)
+
 
 class Building(LevelGeometryMixin, models.Model):
     """
diff --git a/src/c3nav/mapdata/models/geometry/space.py b/src/c3nav/mapdata/models/geometry/space.py
index bc070084..0360579d 100644
--- a/src/c3nav/mapdata/models/geometry/space.py
+++ b/src/c3nav/mapdata/models/geometry/space.py
@@ -5,6 +5,7 @@ from shapely.geometry import CAP_STYLE, JOIN_STYLE, mapping
 from c3nav.mapdata.fields import GeometryField
 from c3nav.mapdata.models.geometry.base import GeometryMixin
 from c3nav.mapdata.models.locations import SpecificLocation
+from c3nav.mapdata.render.cache import changed_geometries
 from c3nav.mapdata.utils.json import format_geojson
 
 
@@ -28,6 +29,21 @@ class SpaceGeometryMixin(GeometryMixin):
                 result['color'] = color
         return result
 
+    def register_change(self, force=True):
+        space = self.space
+        if force or self.geometry_changed:
+            changed_geometries.register(space.level_id, space.geometry.intersection(
+                self.geometry if force else self.get_changed_geometry()
+            ))
+
+    def register_delete(self):
+        space = self.space
+        changed_geometries.register(space.level_id, space.geometry.intersection(self.geometry))
+
+    def save(self, *args, **kwargs):
+        self.register_change()
+        super().save(*args, **kwargs)
+
 
 class Column(SpaceGeometryMixin, models.Model):
     """
diff --git a/src/c3nav/mapdata/models/locations.py b/src/c3nav/mapdata/models/locations.py
index 7e03b145..f9d415a0 100644
--- a/src/c3nav/mapdata/models/locations.py
+++ b/src/c3nav/mapdata/models/locations.py
@@ -160,6 +160,10 @@ class LocationGroupCategory(TitledMixin, models.Model):
     allow_pois = models.BooleanField(_('allow pois'), db_index=True, default=True)
     priority = models.IntegerField(default=0, db_index=True)
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.orig_priority = self.priority
+
     class Meta:
         verbose_name = _('Location Group Category')
         verbose_name_plural = _('Location Group Categories')
@@ -173,6 +177,23 @@ class LocationGroupCategory(TitledMixin, models.Model):
         result.move_to_end('id', last=False)
         return result
 
+    def register_changed_geometries(self):
+        from c3nav.mapdata.models.geometry.space import SpaceGeometryMixin
+        query = self.locationgroups.all()
+        for model in get_submodels(SpecificLocation):
+            related_name = SpecificLocation._meta.default_related_name
+            query.prefetch_related('locationgroup__'+related_name)
+            if issubclass(model, SpaceGeometryMixin):
+                query = query.select_related('locationgorups__'+related_name+'__space')
+
+        for group in query:
+            group.register_changed_geometries(do_query=False)
+
+    def save(self, *args, **kwargs):
+        if self.priority != self.orig_priority:
+            self.register_changed_geometries()
+        super().save(*args, **kwargs)
+
 
 class LocationGroupManager(models.Manager):
     def get_queryset(self):
@@ -193,6 +214,12 @@ class LocationGroup(Location, models.Model):
         default_related_name = 'locationgroups'
         ordering = ('-category__priority', '-priority')
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.orig_priority = self.priority
+        self.orig_category = self.category
+        self.orig_color = self.color
+
     def _serialize(self, **kwargs):
         result = super()._serialize(**kwargs)
         result['category'] = self.category_id
@@ -212,6 +239,21 @@ class LocationGroup(Location, models.Model):
             attributes.append(_('internal'))
         return self.title + ' ('+', '.join(str(s) for s in attributes)+')'
 
+    def register_changed_geometries(self, do_query=True):
+        from c3nav.mapdata.models.geometry.space import SpaceGeometryMixin
+        for model in get_submodels(SpecificLocation):
+            query = getattr(self, SpecificLocation._meta.default_related_name).objects.all()
+            if do_query:
+                if issubclass(model, SpaceGeometryMixin):
+                    query = query.select_related('space')
+            for obj in query:
+                obj.register_change(force=True)
+
+    def save(self, *args, **kwargs):
+        if self.orig_color != self.color or self.priority != self.orig_priority or self.category != self.orig_category:
+            self.register_changed_geometries()
+        super().save(*args, **kwargs)
+
 
 class LocationRedirect(LocationSlug):
     target = models.ForeignKey(LocationSlug, related_name='redirects', on_delete=models.CASCADE,
diff --git a/src/c3nav/mapdata/models/update.py b/src/c3nav/mapdata/models/update.py
index 5652359e..386c8288 100644
--- a/src/c3nav/mapdata/models/update.py
+++ b/src/c3nav/mapdata/models/update.py
@@ -50,8 +50,10 @@ class MapUpdate(models.Model):
             raise TypeError
 
         from c3nav.mapdata.models import AltitudeArea
+        from c3nav.mapdata.render.cache import GeometryChangeTracker
         from c3nav.mapdata.render.base import LevelRenderData
         AltitudeArea.recalculate()
+        GeometryChangeTracker()
         LevelRenderData.rebuild()
         super().save(**kwargs)
         cache.set('mapdata:last_update', (self.pk, self.datetime), 900)
diff --git a/src/c3nav/mapdata/render/cache.py b/src/c3nav/mapdata/render/cache.py
new file mode 100644
index 00000000..66dd6aee
--- /dev/null
+++ b/src/c3nav/mapdata/render/cache.py
@@ -0,0 +1,53 @@
+from django.db.models.signals import m2m_changed, post_delete
+
+from c3nav.mapdata.utils.models import get_submodels
+
+
+class GeometryChangeTracker:
+    def __init__(self):
+        self._geometries_by_level = {}
+        self._deleted_levels = set()
+
+    def register(self, level_id, geometry):
+        self._geometries_by_level.setdefault(level_id, []).append(geometry)
+
+    def level_deleted(self, level_id):
+        self._deleted_levels.add(level_id)
+
+    def reset(self):
+        self._geometries_by_level = {}
+        self._deleted_levels = set()
+
+
+changed_geometries = GeometryChangeTracker()
+
+
+def geometry_deleted(sender, instance, **kwargs):
+    instance.register_delete()
+
+
+def locationgroup_changed(sender, instance, action, reverse, model, pk_set, using, **kwargs):
+    if action not in ('post_add', 'post_remove', 'post_clear'):
+        return
+
+    if not reverse:
+        instance.register_change(force=True)
+    else:
+        if action not in 'post_clear':
+            raise NotImplementedError
+        query = model.objects.filter(pk__in=pk_set)
+        from c3nav.mapdata.models.geometry.space import SpaceGeometryMixin
+        if issubclass(model, SpaceGeometryMixin):
+            query = query.select_related('space')
+        for obj in query:
+            obj.register_change(force=True)
+
+
+def register_signals():
+    from c3nav.mapdata.models.geometry.base import GeometryMixin
+    for model in get_submodels(GeometryMixin):
+        post_delete.connect(geometry_deleted, sender=model)
+
+    from c3nav.mapdata.models.locations import SpecificLocation
+    for model in get_submodels(SpecificLocation):
+        m2m_changed.connect(locationgroup_changed, sender=model.groups.through)
diff --git a/src/c3nav/mapdata/views.py b/src/c3nav/mapdata/views.py
index 9cc2404e..2b6b21f9 100644
--- a/src/c3nav/mapdata/views.py
+++ b/src/c3nav/mapdata/views.py
@@ -9,6 +9,11 @@ from c3nav.mapdata.render.svg import SVGRenderer
 
 
 def tile(request, level, zoom, x, y, format):
+    import cProfile
+    import pstats
+    pr = cProfile.Profile()
+    pr.enable()
+
     zoom = int(zoom)
     if not (0 <= zoom <= 10):
         raise Http404
@@ -72,6 +77,12 @@ def tile(request, level, zoom, x, y, format):
     else:
         data = f.read()
 
+    pr.disable()
+    s = open('/tmp/profiled', 'w')
+    sortby = 'cumulative'
+    ps = pstats.Stats(pr, stream=s).sort_stats(sortby)
+    ps.print_stats()
+
     response = HttpResponse(data, content_type)
     response['ETag'] = etag
     response['Cache-Control'] = 'no-cache'