Ssj40141 920..929

The paper suggests a methodological framework for evaluating adequacy and usability of soil maps by analyzing the following 10 aspects: lineage, consistency, completeness, effective scale, attribute accuracy, thematic contrast, accuracy of legends, integrity, popularity, and accessibility. This framework was used to evaluate the national soil resource inventory in Croatia and to find out why the maps are not used to the full potential. Six 1:50K map sheets (of 185 in total), 3 control surveys, and 10 full profile descriptions in the main landscape regions of Croatia were used to estimate the effective map scale and thematic accuracy of profile observations. In addition, the existing digital data sets (digital soil map and database with 2198 profiles) were evaluated for thematic purity and contrast. The results show that the soil maps are of lower quality than planned and that their usability for spatial planning is limited. The average polygon size and the positional accuracy of primary soil boundaries correspond to the 1:150K scale, while the intensity of field observations corresponds to the 1:250K scale. Mapping units are heterogeneous for mapping of clay content, pH, and organic matter, with an average normalized variation of 68% within units and the mean thematic overlap of 66% between geographically adjacent units. This makes this inventory adequate for small-scale applications only. The major usability problems identified were lack of specific interpretations corresponding to user needs, unpopularity of soil survey concepts, inconsistency of methodology and unclear distribution policy. The evaluation can be used to decide how to improve the usability of the existing datasets and design methodological steps for a new survey by involving end users in the design of the soil information system. SEVERAL STUDIES in the past 30 yr have shown that the technical quality and usability of soil maps, especially the ones produced through national soil surveys, has often been overestimated or neglected. Marsman and de Gruijter (1986) showed that the actual purity of soil mapping units in the Netherlands is usually considerably lower than the anticipated level of 70%. Groot (1993) estimated that 80% of soil information in the world is unusable due to incompleteness, unknown reliability, or inconsistant spatial referencing. A major problem of assessing the quality of soil maps is that, typically, the same teams that make the original surveys are responsible for adequacy evaluation. In the USA, quality control and quality assurance are increasingly being arranged by an external and unbiased team (USDA–NRCS, 2003; Part 609), which is not the case of most other countries in the world. A general impression is that the quality issue of soil maps has been underrepresented in the literature and definitively deserves more exposure (Bishop et al., 2001). Five main elements determine the overall quality of a map: lineage, positional and attribute accuracy, logical consistency, and completeness. These correspond to the quality measures and standards approved by the International Cartography Association and applicable to any GIS (Guptill and Morrison, 1995). Soil surveyors have developed a concept of adequacy of a soil resource inventory, which was first introduced by a group at Cornell University (Forbes et al., 1982). This group proposed that adequacy should be evaluated using four aspects: (1) map scale and texture, (2) map legend, (3) base map quality, and (4) ground truth, also called thematic accuracy. The last aspect has attracted attention of Dutch mappers (de Gruijter andMarsman, 1985; Marsman and de Gruijter, 1986). Recently, the concept of spatial data usability, of which data quality is considered to be just one element, has been introduced (Wachowicz et al., 2002; Hunter et al., 2003). There are four general aspects of usability: (i) data quality (accuracy, completeness, logical consistency); (ii) data form(at); (iii) data accessibility and price, and (iv) quality of the metadata. The importance of each of these aspects may differ from user to user. For example, for environmental modelers, the incompatibility, low thematic contrast and detail of multisource environmental geo-data will militate against their full usage. The difference between quality, adequacy, and usability is that quality is a set of constant technical characteristics, adequacy changes within the problemsolving context, while usability reflects all these elements in relation to the end-user satisfaction. Adequacy is related to the concept of effective scale—a less detailed soil map will show higher adequacy if used at smaller scales. Although usability is in practice hard to measure, Hunter et al. (2003) suggested some very concrete aspects of usability, such as data integrity, popularity, satisfaction, speed of access, reliability etc., which can be either measured directly or assessed through interviews. Soil mappers will increasingly need to find a balance between the availability of funds, models, tools, and users’ demands. In fact, the key challenge to future soil mapping projects will be to fully identify and meet customers’ needs (Indorante et al., 1996) and provide a T. Hengl, European Commission, Directorate General JRC, Land Management and Natural Hazards Unit, Ispra (VA), Italy; S. Husnjak, Soil Science Dep., Faculty of Agriculture, Univ. of Zagreb, Svetošimunska 25, 10000 Zagreb, Croatia. Received 19 Apr. 2004. *Corresponding author ([email protected]). Published in Soil Sci. Soc. Am. J. 70:920–929 (2006). Pedology doi:10.2136/sssaj2004.0141 a Soil Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: AD, area of disagreement; ASD, average size delineation; BSMC, Basic Soil Map of Croatia; CYS, Classification of Yugoslav Soils; ESN, effective scale number; GIS, Geographic Information System; ILWIS, Integrated Land and Water Information System; IMR, index of maximum reduction; ISRIC, International Soil and Reference Information Centre; ME, mean absolute error; MLD, minimum legible delineation; RMSE, root mean square error; SIS, Soil Information System; SMU, soil mapping units. R e p ro d u c e d fr o m S o il S c ie n c e S o c ie ty o f A m e ri c a J o u rn a l. P u b lis h e d b y S o il S c ie n c e S o c ie ty o f A m e ri c a . A ll c o p y ri g h ts re s e rv e d . 920 Published online April 19, 2006