Productive capacity depends largely on the physical qualities of the land, soil and the environment. These physical qualities are frequently far from ideal. Differences between ideal and actual may be regarded as limitations imposed by the physical qualities of the soil, and the environment. These limitations affect productivity, the number and complexity of corrective practices needed, and the intensity and manner of land use. Limitations include susceptibility to erosion, steepness of slope, susceptibility to flooding, liability to wetness or drought, salinity, depth of soil, soil texture, structure and nutrient supply and climate.

Assessment of land for long-term sustained production is based on an interpretation of the physical information in a Land Resource Inventory (LRI), which is compiled from a field assessment of rock types, soils, landform and slopes, erosion types and severities, and vegetation cover. Land Resource Inventory is supplemented with information on climate, flood risk, erosion history and the effects of past practices.

The extended legends (National or regional) greatly assist a LUC mapper in recognising the productive potential of a mapped unit (polygon).  If the LUC mapper can accurately define the extent of map units and correctly assign the various inventory factors to those map units, the task of then assigning a LUC unit code (LUC class, subclass and unit code) to each map unit is greatly simplified.  Having correctly assigned the LUC unit code, further reference to the regional legends and regional bulletins will reveal more detailed information about the expected productive potential of that map unit.