QUALITY CONTROL IN SOIL SURVEY INTRODUCTION: I. THE CHOICE OF MAPPING UNIT

THE QUALITY OF A SOIL MAP DEPENDS ON ITS UTILITY FOR PRACTICAL PURPOSES AND SHOULD BE JUDGED BY THIS STANDARD. THIS SERIES SUGGESTS HOW UTILITY MAY BE MEASURED, AND BRIEFLY LISTS THE PLANNING AND EXECUTION OF A SOIL SURVEY WHICH DETERMINES THE UTILITY OF THE RESULTING SOIL MAP. SUBSEQUENT PAPERS IN THE SERIES DISCUSS THEIR INFLUENCE SEPARATELY. PART I DISCUSSES THE POLICY DECISION ON THE KIND OF MAPPING UNIT. IT REVIEWS DIFFERENT KINDS OF MAPPING UNITS AND PRESENTS A SCORING PROCEDURE TO COMPARE THE CEILINGS WHICH EACH IMPOSES ON THE UTILITY OF A SOIL MAP. THE SCORING PROCEDURE ASSUMES THAT THE WHOLE EXTENT OF EVERY MAPPED SOIL UNIT EXACTLY MATCHES ITS DESCRIPTION IN THE MAP LEGEND. ON THIS BASIS IT ESTIMATES THE AVERAGE PROBABILITY THAT THE SOIL PROFILE CLASS AT ANY RANDOMLY LOCATED SITE WITHIN A SURVEY AREA IS CORRECTLY PREDICTED. THE SCORE IS A CEILING, ATTAINABLE ONLY IF THE EXECUTION OF THE SURVEY WERE PERFECT, AND NO MAPPING UNIT CONTAINED PROFILE CLASSES NOT PREDICTED FROM ITS LEGEND. EVEN SO THE LEGENDS OF MANY PUBLISHED SOIL MAPS ACHIEVE SCORES OF 50 PER CENT OR LESS. THE PAPER STRESSES THE IMPORTANCE OF ADEQUATE AIDS TO PREDICT THE OCCURRENCE OF INDIVIDUAL PROFILE CLASSES WITHIN COMPOUND MAPPING UNITS CONTAINING MORE THAN ONE. THESE POINTS ARE ILLUSTRATED FROM AUSTRALIAN EXPERIENCE. /TRRL/A/