The World Reference Base for Soil Resources (WRB) is the soil classification system endorsed by the International Union of Soil Science (IUSS). It was designed to faciliate correlation of soil individuals and thus studies of soil properties and function across national boundaries. The WRB is ideally suited to discussing soil properties, function, use potential and genesis at world or regional scale. It was not intended to provide names for map units, especially for the large-scale mapping necessary in urban areas.

The WRB is a two-level classification: (1) Thirty-one (31) Reference Groups which have major differences in terms of pedogenesis, geography, and use potential; (2) a list of prefix and suffix qualifiers for each Reference Group which can be added to the group name to indicate detailed soil properties.

Historically, built areas were ignored in soil mapping and in studies of soil formation and behaviour. It is now recognized that these areas are of prime importance to human populations. Another trend is the large increase in reclaimed lands and new uses for old industrial areas. In many countries there are active projects to map such areas, either with locally-developed classification systems or ad-hoc names. It should be possible to use the WRB to correlate local efforts in urban & industrial soil studies. However, the original WRB (1998) and its predecessor FAO map legends (1974, 1990) were developed with concepts from national classifications and pedogenetic studies that were skewed in favour of rural soils, so that some of the names that were assigned to urban soils were not very connotative.

Similar issues with anthropogenic soils of intensively-farmed rural areas led the appointment of two WRB working groups, one for urban soils and one for anthropogenic soils, commonly called the "Technosol" and "Anthrosol" working groups, respectively. The aim was to propose changes to the WRB to better classify urban and industrial soils, keeping in mind the intended role and current structure of the WRB. A wide consultation led to a majority proposal, with some minority opinions, presented to the WRB Commission in December 2005; these were taken into account in the WRB 2006 presented at this Congress.

The most far-reaching change is the introduction of a 31^st Reference Group: the Technosols, whose central concept is dominance of soil properties and function by technical human activity as evidenced by one of: (1) substantial presence of artefacts, defined as material created or substantially modified by humans as part of an industrial or artisanal manufacturing process and with more or less their original properties; or (2) a nearly continuous impermeable, constructed geomembrane ("liner"); or (3) technic hard rock ("pavement"). Artefacts also include material excavated from a depth where they were not influenced by surface processes, with properties substantially different from the environment where they are placed. Thus fresh mine spoil is a Technosol but freshly-dumped overburden is a Regosol.

A difficulty with identifying Technosols in the field is the requirement that the technic nature dominate any subsequent pedogenesis. At one extreme is fresh pavement, at the other a Roman road which over the years has developed a strong mollic horizon and whose continuous dressed-stone pavement has been disrupted by frost, animals, or tree roots; the first is a Technosol, the latter not. The phrase "substantially the same properties as when first manufactured, modified or excavated" must be documented by the classifier.

Urban areas contain many soils from "rural" Reference Groups, especially in parks and unbuilt areas, but most of these show significant effects from their urban environment. Second-level qualifiers have been introduced to indicate some of these, e.g. densic for strong compaction. However, if WRB names are to be used for mapping urban soils, much more detail is needed; this can be provided by naming and characterising the substrate, detailed profile morphology, and phases to specify anthrogeomorpholgy (land form as influenced by humans) and soil constituents, especially pollutants.