Abstract:

【Background】 Soil large data with time and space dimension, could provide data support for research work and policy decision in agriculture, environment, and land management. The soil survey maps and reports are the base on building soil time and space database. Because of the large differences of soil mapping standards between different areas and different periods, quality control is necessary for developing high quality soil database from non-standard soil maps and soil survey reports. 【Objective】 The purpose of this study was to analyze the status of paper soil maps, to identify the key issues of quality control in its digital integration database, and to explore the corresponding technical standards and specifications, so as to provide quality guarantee for large scale soil map database. 【Method】 By analyzing the situation of soil maps and soil survey reports and combining related research for precision control of digital topographic map in China, precision requirements suitable for digitizing soil map were developed. After comparing soil type names from county level soil maps and soil standard names in national standard, soil names, especially soil great group names, were revised in soil map database and every soil name was encoded. 【Result】 For building soil map database from different sources large scale soil maps in large area, the quality control included the geographic precision, standardization of digital soil map elements, integration of soil map database, and coding elements type for the whole database. The contents of geographic precision included scanning precision of paper maps, coordinate system, geometric correction precision, as well as collection and numbers of control points. Standardization of map elements extraction mainly included the collection of soil elements and non-soil elements, classification and code of digital element types, and standard of layer name and map sheets. The integration for whole database included revision of soil types, code of soil types and non-soil types, and standard of boundary by using uniform boundary. In the process of soil data integration and harmonization, revising soil names, especially revising soil great group names and coding, was the mainly quality control method. According to national standard and soil profile records in soil survey reports of county, province and national level for reference, more than 300 non-standard soil great group names were revised to 60 national standard names. By hierarchical code method, a unique code for each soil type in the entire database was achieved with five-level coding of soil order, soil great group to soil species. Using uniform boundary, the boundaries of adjacent counties were seamless. Based on the integration of the entire soil special database, the conversion were achieved from counties map sheet to international standard map sheet at 1:50 000. 【Conclusion】 The quality control is very important in building soil map database of large area by using non-standard soil maps from different region and period. The key of quality control were geographic precision, standardization of digital soil map elements, integration of soil map database and coding soil types for the entire database. The quality control methods and corresponding indicators for these three issues conformed to the actual situation of soil survey maps in China. Using the above methods, the 1:50 000 soil map database had a total 13 240 standard map sheets of 1:50 000 scale, and involving 1 688 counties and county farms. In addition, we discussed the status of this database and prospected the future direction for expansion, in the hope that to provide a data basis for the study of the long-term soil properties data mining by combining the physical and chemical properties of the soil.

Key words: 1:50 000 scale soil map, digital, database, quality control, China