A Purposive Sampling Design Method Based on Typical Points and Its Application in Soil Mapping
Online published: 2010-03-25
In consideration of limitations of classical sampling and spatial sampling, this paper proposed a purposive sampling method based on typical points. This method employed environmental factors which co-vary the target geographical element to find typical patterns of the geographical element over space. Field samples were then designed based on the locations of these typical patterns. It is believed that these field samples capture the overall pattern of spatial variation of the target variable well. With this approach, the number of field samples needed to characterize the spatial pattern of the target variable was reduced. The approach was applied in two study areas in Heshan Farm in Heilongjiang Province of China. Two soil properties were chosen, i.e. A-horizon organic matter and soil thickness (each property for one study area). Environmental combinations were generated by a fuzzy c-means clustering on four local environmental data layers and typical points were then designed with help of fuzzy membership maps of environmental combinations. Spatial variation of the two soil properties was inferred using a linear weighted average model with typical points’ soil property values and fuzzy membership maps of environmental combinations. The mapping results reflected continuous changing of soil properties with terrain changing. Four indices were set up for evaluation of mapping results by using independently validation points. The evaluation results showed that, the agreement coefficients between observed values and predicted values of validation points were high for both of the study areas. We then concluded that the proposed sampling design approach was effective. Analysis was also conducted on difference between soil property mapping results by using different amount of typical points when different number of typical points representing each environmental combination. It was showed that using more points would not necessarily result in a more accurate map.
YANG Lin1, ZHU A-Xing1, QIN Chengzhi1, LI Baolin1, PEI Tao1, QIU Weili2, XU Zhig . A Purposive Sampling Design Method Based on Typical Points and Its Application in Soil Mapping[J]. PROGRESS IN GEOGRAPHY, 2010 , 29(3) : 279 -286 . DOI: 10.11820/dlkxjz.2010.03.004
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