diff --git a/lambdas/preprocessing/src/lambda_function.py b/lambdas/preprocessing/src/lambda_function.py
index b5e1a33..4c0b556 100644
--- a/lambdas/preprocessing/src/lambda_function.py
+++ b/lambdas/preprocessing/src/lambda_function.py
@@ -32,42 +32,47 @@ def handler(event: Dict[str, Any], context: Any) -> Any:
         LOGGER.info(f"Running preprocessing with parameters: {event}")
         fc: Optional[Dict] = event.get("feature_collection")
         uri: Optional[str] = event.get("uri")
-        id_field = event.get("id_field", "fid")
+        geostore_ids: Optional[List[str]] = event.get("geostore_ids")
+        id_field: Optional[str] = event.get("id_field", "fid")
 
-        if fc is not None and uri is not None:
-            raise Exception("Please specify GeoJSON via (only) one parameter!")
+        if (fc and uri) or (fc and geostore_ids) or (uri and geostore_ids):
+            raise Exception("Please specify exactly one of 'feature_collection', 'uri', or 'geostore_ids'.")
         elif fc is not None:
-            gpdf = gpd.GeoDataFrame.from_features(fc)
+            gpdf = gpd.GeoDataFrame.from_features(fc, columns=[id_field, "geometry"])
         elif uri is not None:
-            gpdf = gpd.read_file(uri)
+            gpdf = gpd.read_file(uri, columns=[id_field, "geometry"])
+        elif geostore_ids is not None:
+            geostore_info = get_geostore_geoms(geostore_ids)
         else:
-            raise Exception("Please specify GeoJSON via (only) one parameter!")
+            raise Exception("Please specify exactly one of 'feature_collection', 'uri', or 'geostore_ids'.")
 
-        if id_field not in gpdf.columns.tolist():
+        if gpdf is not None and id_field not in gpdf.columns.tolist():
             raise Exception(f"Input feature collection is missing ID field '{id_field}'")
 
-        columns = gpdf.columns.tolist()
-        hasGeo = "geometry" in columns
-        hasGeoId = "geostore_id" in columns
-        if (not hasGeo and not hasGeoId) or (hasGeo and hasGeoId):
-            raise Exception("Input feature collection must have exactly one of 'geometry' or 'geostore_id'")
-
-        geostore_geoms: List[Dict[str, Any]]
-        if hasGeoId:
-            geostore_ids: List[str] = []
+        rows: List[List[str]] = []
+        if geostore_info is not None:
+            for info in geostore_info:
+                # Use the geostoreId itself as the id field for the output.
+                id = info["geostoreId"]
+                # The RW find-by-ids call returns the geometry as a feature collection,
+                # which I think should always have one feature (?)
+                fc = info["geostore"]["data"]["attributes"]["geojson"]["features"]
+                if fc is None:
+                    raise Exception(f"Missing features attribute for geostore '{id}'")
+                # GeoDataFrame.from_features() expects each feature to have a
+                # 'properties' field.
+                for f in fc:
+                    if f.get("properties") is None:
+                        f["properties"] = {}
+                minidf = gpd.GeoDataFrame.from_features(fc)
+                geom = shape(getattr(minidf.iloc[0], "geometry"))
+                encoded_geom = encode_geometry(geom)
+                rows.append([id, encoded_geom])
+        else:
             for record in gpdf.itertuples():
-                geostore_ids.append(getattr(record, "geostore_id"))
-            geostore_geoms = get_geostore_geoms(geostore_ids)
-
-        rows = []
-        for (i, record) in enumerate(gpdf.itertuples()):
-            if hasGeoId:
-                minidf = gpd.GeoDataFrame.from_features(geostore_geoms[i]["geostore"]["data"]["attributes"]["geojson"]["features"])
-                geom = shape(getattr(minidf.head(), "geometry"))
-            else:
                 geom = shape(getattr(record, "geometry"))
-            encoded_geom = encode_geometry(geom)
-            rows.append([getattr(record, id_field), encoded_geom])
+                encoded_geom = encode_geometry(geom)
+                rows.append([getattr(record, id_field), encoded_geom])
 
         # Consider replacing UUID with hash of args for cacheability
         request_hash: UUID = uuid4()