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 mineralogical 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 particle size classification attribute. Particle size class describes in broad terms the proportions of sand, silt and clay in the fine earth fraction of the soil except in the case of skeletal soils ( > 35% coarse fraction ) where it applies to the whole soil. The classes are described in Webb and Wilson (1995) and the user should also refer to the item grav_class for a description of the topsoil gravel content of soils. For the 2nd Edition Gisborne-East Coast mapping, particle size is recorded as undefined as soils were mapped directly to the New Zealand Soil Classification.
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.