{'fraction_non_alphanumeric': 0.019450800915331808, 'fraction_numerical': 0.012585812356979404, 'mean_word_length': 5.7011494252873565, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Optimizing the Size of Spatial Sampling Units for Estimating Winter Wheat Sown Acreage

The formulation of sampling unit size is essential in spatial sampling schemes for estimating crop sown area.Reasonable sampling unit size plays an important role for reducing sampling cost and improving population extrapolation accuracy.The experiment on optimizing sampling unit size was conducted to improve the efficiency of spatial sampling for winter wheat sown acreage estimation.Henan Province was selected as a study area and square grids as sampling units.Following the principle that sampled units are independent each other,sampling unit size is preliminarily selected through analyzing the relationships between different sampling unit sizes and corresponding global spatial autocorrelation index(Moran's I) of all population units in the sampling frame.Furthermore,in order to find the optimal sampling unit size,eight kinds of sampling frames are constructed using the preliminarily selected sampling unit sizes and stratified sampling method.The stratification symbol is the ratio of winter wheat sown area accounting for that of a sampling unit,which is used to draw samples,and then extrapolate population value as well as estimate sampling errors.The experimental results demonstrate that,sampling fraction increases with the increase of sampling unit size;both the relative errors and coefficients of variation(CV) of population extrapolation are small at eight sampling unit size levels(relative errors vary from 3.82% to 5.75%,CV vary from 3.76% to 4.69%).It is found that the efficiency of stratified sampling method used to estimate the population of winter wheat sown area is the maximum,when the sampling unit size is 20000 m×20000 m.