the degree to which a particular trade is free to move is obviously of prime importance in the proper consideration of any town planning scheme which involves a re-siting of industry, however long-term the scheme or gradual the proposed re-siting may be. We have seen something of the factors which have operated in a particular group of industries in the past and it now remains to examine industry as a whole, so that we can get an overall picture of the degree to which it is theoretically * possible to move industry and the factors which have affected its location in the past and are likely to affect it in the future.