We performed a systematic mapping of validation methods used in digital soil mapping (DSM), in order to gain an overview of current practices and make recommendations for future publications on DSM studies. A systematic search and screening procedure, largely following the RepOrting standards for Systematic Evidence Syntheses (ROSES) protocol, was carried out. It yielded a database of 188 peer‐reviewed DSM studies from the past two decades, all written in English and all presenting a raster map of a continuous soil property. Review of the full‐texts showed that most publications (97%) included some type of map validation, while just over one‐third (35%) estimated map uncertainty. Most commonly, a combination of multiple (existing) soil sampe datasets was used and the resulting maps were validated by single data‐splitting or cross‐validation. It was common for essential information to be lacking in method descriptions. This is unfortunate, as lack of information on sampling design (missing in 25% of 188 studies) and sample support (missing in 45% of 188 studies) makes it difficult to interpret what derived validation metrics represent, compromising their usefulness. Therefore, we present a list of method details that should be provided in DSM studies. We also provide a detailed summary of the 28 validation metrics used in published DSM studies, how to interpret the values obtained and whether the metrics can be compared between datasets or soil attributes.

中文翻译：

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连续属性数字土壤制图中验证的观点—综述

我们对数字土壤测绘（DSM）中使用的验证方法进行了系统的测绘，以便获得当前实践的概述并为DSM研究的未来出版物提供建议。系统的搜索和筛选程序，主要遵循系统证据合成的RepOrting标准（ROSES）协议。它产生了一个数据库，该数据库包含过去20年中188项经过DSM同行评审的研究，所有研究都是用英语编写的，并且都提供了连续土壤特性的栅格图。对全文的审查表明，大多数出版物（97％）都包含某种类型的地图验证，而估计的地图不确定性仅超过三分之一（35％）。最常见的是，使用多个（现有）土壤样本数据集的组合，并且通过单个数据拆分或交叉验证来验证生成的图。方法描述中缺少基本信息是很常见的。不幸的是，由于缺乏有关样本设计的信息（188个研究中的25％缺少）和样本支持（188个研究中的45％缺少），使得难以解释衍生的验证指标代表什么，从而损害了其实用性。因此，我们列出了DSM研究中应提供的方法详细信息列表。我们还提供了已发布的DSM研究中使用的28种验证指标的详细摘要，如何解释所获得的值，以及这些指标是否可以在数据集或土壤属性之间进行比较。