diff --git a/src/c3nav/mapdata/cache.py b/src/c3nav/mapdata/cache.py
index 66dd6aee..5f70696b 100644
--- a/src/c3nav/mapdata/cache.py
+++ b/src/c3nav/mapdata/cache.py
@@ -1,8 +1,96 @@
+import math
+import struct
+
+import numpy as np
+from django.conf import settings
 from django.db.models.signals import m2m_changed, post_delete
+from shapely import prepared
+from shapely.geometry import box
 
 from c3nav.mapdata.utils.models import get_submodels
 
 
+class MapHistory:
+    # binary format (everything little-endian):
+    # 1 byte (uint8): resolution
+    # 2 bytes (uint16): origin x
+    # 2 bytes (uint16): origin y
+    # 2 bytes (uint16): origin width
+    # 2 bytes (uint16): origin height
+    # 2 bytes (uint16): number of updates
+    # n*16 bytes: update keys as null-terminated strings
+    # width*height*2 bytes: data (line after line) with uint16 data
+
+    def __init__(self, resolution=settings.CACHE_RESOLUTION, x=None, y=None, updates=None, data=None):
+        self.resolution = resolution
+        self.x = None
+        self.y = None
+        self.updates = updates
+        self.data = data
+        self.unfinished = False
+
+    @classmethod
+    def open(cls, filename, default_update=None):
+        try:
+            with open(filename, 'rb') as f:
+                resolution, x, y, width, height, num_updates = struct.unpack('<BHHHHH', f.read(11))
+                updates = list(struct.unpack('16s'*num_updates, f.read(num_updates*16)))
+                data = np.frombuffer(f.read(width*height*2), np.uint16).reshape((height, width))
+                return cls(resolution, x, y, list(updates), data)
+        except FileNotFoundError:
+            if default_update is None:
+                raise
+            return cls(updates=[default_update])
+
+    def save(self, filename):
+        with open(filename, 'wb') as f:
+            f.write(struct.pack('<BHHHHH', self.resolution, self.x, self.y, *reversed(self.data.shape),
+                                len(self.updates)))
+            f.write(struct.pack('16s'*len(self.updates), *self.updates))
+            f.write(self.data.tobytes('C'))
+
+    def add_new(self, geometry):
+        prep = prepared.prep(geometry)
+        minx, miny, maxx, maxy = geometry.bounds
+        res = self.resolution
+        minx = int(math.floor(minx/res))
+        miny = int(math.floor(miny/res))
+        maxx = int(math.ceil(maxx/res))
+        maxy = int(math.ceil(maxy/res))
+
+        data = self.data
+        if self.resolution != settings.CACHE_RESOLUTION:
+            data = None
+            self.updates = self.updates[-1:]
+
+        if data is None:
+            data = np.zeros(((maxy-miny), (maxx-minx)), dtype=np.uint16)
+            self.x, self.y = minx, miny
+        else:
+            orig_height, orig_width = data.shape
+            if minx < self.x or miny < self.y or maxx > self.x+orig_width or maxy > self.y+orig_height:
+                new_x, new_y = min(minx, self.x), min(miny, self.y)
+                new_width = min(maxx, self.x+orig_width)-new_x
+                new_height = min(maxy, self.y+orig_height)-new_y
+                new_data = np.zeros((new_height, new_width), dtype=np.uint16)
+                dx, dy = new_x-self.x, new_y-self.y
+                new_data[dy:dx, (dy+orig_height):(dx+orig_width)] = data
+                data = new_data
+                self.x, self.y = new_x, new_y
+
+        new_val = len(self.updates)
+        for iy, y in enumerate(range(miny*res, maxy*res, res), start=miny-self.y):
+            for ix, x in enumerate(range(miny*res, maxy*res, res), start=minx-self.x):
+                if prep.intersects(box(x, y, x+res, y+res)):
+                    data[iy, ix] = new_val
+
+        self.unfinished = True
+
+    def finish(self, cache_key):
+        self.unfinished = False
+        self.updates.append(cache_key)
+
+
 class GeometryChangeTracker:
     def __init__(self):
         self._geometries_by_level = {}
diff --git a/src/c3nav/settings.py b/src/c3nav/settings.py
index 422db2fd..76d426b9 100644
--- a/src/c3nav/settings.py
+++ b/src/c3nav/settings.py
@@ -59,6 +59,7 @@ DEBUG = config.getboolean('django', 'debug', fallback=debug_fallback)
 RENDER_SCALE = float(config.get('c3nav', 'render_scale', fallback=20.0))
 SVG_RENDERER = config.get('c3nav', 'svg_renderer', fallback='rsvg-convert')
 CACHE_TILES = config.get('c3nav', 'cache_tiles', fallback=not DEBUG)
+CACHE_RESOLUTION = config.get('c3nav', 'cache_resolution', fallback=4)
 
 db_backend = config.get('database', 'backend', fallback='sqlite3')
 DATABASES = {