def crop_cmd(crop, last_output, expected_output):
	"""Command to crop OSM file by area.

	>>> crop_cmd('my_area.geojson', 'file1.osm', 'file2.osm.pbf')
	('osmium extract file1.osm -o file2.osm.pbf -p "my_area.geojson"', None)
	"""
	return f'osmium extract {last_output} -o {expected_output} -p "{crop}"', None