All titles, estates, rights and interests in airspace are subject to taxation to the same extent and in the same manner as other real property is taxed; and for the purpose of taxation, titles, estates, rights and interests in airspace held by persons other than by the owner or owners of the land surface shall be taxed separately from the land surface and from other separately owned airspace, and the owner or owners of the land surface shall not be taxed for airspace which is not owned, nor to the extent that his or their rights therein have been diminished. Nothing contained in this section shall be construed to authorize taxation of unimproved or undeveloped airspace either by adding to the assessed valuation of the surface or by taxation on said unimproved or undeveloped airspace itself. This act shall not apply to aviation, air or space travel.