fix multi-geometry issue

app.py

@@ -22,6 +22,11 @@ def preprocess_gdf(gdf):
     return gdf
 
 
+def is_valid_polygon(geometry_gdf):
+    geometry = geometry_gdf.geometry.item()
+    return (geometry.type == "Polygon") and (not geometry.is_empty)
+
+
 # wide streamlit display
 st.set_page_config(layout="wide")
 
@@ -72,6 +77,15 @@ else:
     input_gdf = preprocess_gdf(gpd.read_file(file_url))
     if len(input_gdf) > 1:
         st.warning(f"Only the first polygon in the KML will be processed; all other geometries will be ignored.")
+
+    for i in range(len(input_gdf)):
+        geometry_gdf = input_gdf[input_gdf.index == i]
+        if is_valid_polygon(geometry_gdf):
+            break
+    else:
+        st.error(f"No polygon found inside KML. Please check the KML file.")
+        st.stop()
+
     st.session_state.input_gdf = input_gdf
     # st.toast("Data loaded and cached")