diff --git a/data/ventilation_index_zones.geojson.xz b/data/ventilation_index_zones.geojson.xz
new file mode 100644
index 0000000..584dd28
Binary files /dev/null and b/data/ventilation_index_zones.geojson.xz differ
diff --git a/utils/zones.py b/utils/zones.py
index 297321c..7d50e88 100644
--- a/utils/zones.py
+++ b/utils/zones.py
@@ -1,11 +1,33 @@
+import lzma
+
 from geopandas import read_file, GeoDataFrame
 
+COMPRESSED_FILEPATH = "./data/ventilation_index_zones.geojson.xz"
+DECOMPRESSED_FILEPATH = "./tmp/ventilation_index_zones.geojson"
+
+
+def _compress_ventilation_index_zones():
+    # Git has a filesize limit of 50MB. The shapefile is 60MB, so it should be
+    # compressed at rest.
+    with open(DECOMPRESSED_FILEPATH, "rb") as f_in:
+        bytes = f_in.read()
+    with lzma.open(COMPRESSED_FILEPATH, "w") as f_out:
+        f_out.write(bytes)
+
+
+def _decompress_ventilation_index_zones():
+    with lzma.open(COMPRESSED_FILEPATH, "r") as f_in:
+        bytes = f_in.read()
+    with open(DECOMPRESSED_FILEPATH, "wb") as f_out:
+        f_out.write(bytes)
+
 
-def get_ventilation_index_zones() -> GeoDataFrame:
-    ventilation_index_zones: GeoDataFrame = read_file("./data/ventilation_index_zones.geojson")
+def read_ventilation_index_zones() -> GeoDataFrame:
+    _decompress_ventilation_index_zones()
+    ventilation_index_zones = read_file(DECOMPRESSED_FILEPATH)
     print(f"loaded {ventilation_index_zones.shape[0]} ventilation index zones.")
     return ventilation_index_zones
 
 
 if __name__ == "__main__":
-    get_ventilation_index_zones()
+    read_ventilation_index_zones()