Sub-sampling a large physical soil archive for additional analyses to support spatial mapping; a pre-registered experiment in the Southern Nations, Nationalities, and Peoples Region (SNNPR) of Ethiopia

•Soil physical archives are a valuable resource, and should be used sparingly.•We propose a strategy to subsample an archive from Ethiopia.•A model from cognate landscapes is used to evaluate proposed subsamples.•We publish our criteria to evaluate the strategy before receiving data.