diff --git a/etl/extract_mastermap.py b/etl/extract_mastermap.py
deleted file mode 100644
index c9ac70de..00000000
--- a/etl/extract_mastermap.py
+++ /dev/null
@@ -1,7 +0,0 @@
-"""Extract buildings from *.gml.gz
-
-Features where::
-    descriptiveGroup = '(1:Building)'
-
-Use `fid` as source ID, aka TOID.
-"""
diff --git a/etl/extract_mastermap.sh b/etl/extract_mastermap.sh
new file mode 100644
index 00000000..f6c06238
--- /dev/null
+++ b/etl/extract_mastermap.sh
@@ -0,0 +1,20 @@
+# Extract buildings from *.gml.gz
+#
+# Features where::
+#     descriptiveGroup = '(1:Building)'
+#
+# Use `fid` as source ID, aka TOID.
+
+: ${1?"Usage: $0 ./path/to/input/dir ./path/to/ouput/dir"}
+
+: ${2?"Usage: $0 ./path/to/input/dir ./path/to/ouput/dir"}
+
+find $1 -type f -name '*.gz' -printf "%f\n" | \
+parallel \
+ogr2ogr \
+    -select fid \
+    -where "\"descriptiveGroup='(1:Building)'\"" \
+    -t_srs "EPSG:3857" \
+    -f "GeoJSON" $2/{}.geojson \
+    $1/{} \
+    TopographicArea