def buffer_space(gdf, dist=0, dissolve='week', proj=2163):
	"""
	Perform activity space based on buffer method

	Parameters
	==========
	gdf: GeoDataFrame
	dist: buffer distance in meters
	dissolve: level of aggregating points to form polygon

	Returns
	=======
	gdf: Polygon GeoDataFrame (user-defined projection)
	"""
	# gdf.crs = ("epsg:4326")
	gdf = gdf.to_crs(epsg=proj)
	gdf['geometry'] = gdf.geometry.buffer(dist)
	polys = gdf.dissolve(by=[dissolve]).reset_index()
	polys['buff_area'] = polys['geometry'].area
	return polys