LONDON — Land art is having a moment in the UK. It was building last year with two shows, in Margate and Birmingham, by perambulatory artist Hamish Fulton. More ‘walking art’ is afoot in Sunderland. April found Nancy Holt on show in Manchester. And in maritime city Southampton, we have not one but two land art exhibitions, one of which will take a three stop tour of the region. The genre has nothing if not geographical spread.