The New Zealand Fundamental Soil Layer originates from a relational join of features from two databases: the New Zealand Land Resource Inventory (NZLRI), and the National Soils Database (NSD). The NZLRI is a national polygon database of physical land resource information, including a soil unit. Soil is one in an inventory of five physical factors (including rock, slope, erosion, and vegetation) delineated by physiographic polygons at approximately 1:50,000 scale. The NSD is a point database of soil physical, chemical, and mineralological characteristics for over 1500 soil profiles nationally. A relational join between the NZLRI dominant soil and derivative tables from the NSD was the means by which 14 important soil attributes were attached to the NZLRI polygons. Some if these attributes originate from exact matches with NSD records, while others derive from matches to similar soils or professional estimates. This layer contains the best available data (as at 2000) of Profile Readily Available Water (PRAW) which estimates water readily available to plants for the soil profile to a depth of 0.9 m, or to the potential rooting depth (whichever is the lesser). Values are weighted averages over the specified profile section (0-0.9 m) and are expressed in units of mm of water.
The polygon set used in this layer is equivalent to NZLRI Version 3.1, dissolved on soil. Soil attribute data derive from regional soil legends and the NSD as at 1999 Incidental error correction has occurred as necessary
Accuracy of soil attribute values is dependant on the variability of the soil unit over its entire geographic extent and the origin of the estimate (recorded in the _EST fields)
Polygons derive from the multi-factor, homogenous unit area mapping of the NZLRI. This method often delineates features at a lower resolution than a single factor map of equivalent scale.
While NZLRI mapping scale remained constant (at 1:63,360 and later 1:50,000), polygon resolution increased in detail as the survey progressed, and was variably constrained by the quality of source information available to the mapper