§ 237. Maps and recommendations. Such planning commission may cause to be made a map or maps of said city or village or any portion thereof, or of any land outside the limits of said city or village so near or so related thereto that in the opinion of said planning commission it should be so mapped. Such plans may show not only such matters as by law have been or may be referred to the planning commission, but also any and all matters and things with relation to the plan of said city or village which to said planning commission seem necessary and proper, including recommendations and changes suggested by it; and any report at any time made, may include any of the above. Such planning commission may obtain expert assistance in the making of any such maps or reports, or in the investigations necessary and proper with relation thereto.