A novel spatial statistical method called Single Point Area Estimation (SPA) was developed to estimate an area value based on the observations at a single point observations. The method is applicable to estimate an area value when establishing observation stations are too expensive, or records are rare in ancient time or in remote areas.

The principle of SPA isthat the value at the singlepointwas weighted to estimate the true value of a large area, with an objective function of unbiasedand the least variance of the estimation. After a mathematical derivation, the weight and the error of the estimation are found to be the functions of spatialautocorrelation, and the correlation between the single point value and the entire area value. The correlation coefficients can be approximated by that of an auxiliary variable. The auxiliary variable should be spatiotemporally correlated with the target variable, and should fully coverage the study area and easy to be acquired.

SPA was used to estimate the daily value of citywide PM2.5 concentration inBeijing,based on daily PM2.5 observationsat a single pointin the US Embassy to Beijing,with an auxiliary variable of PM10 observed at 18 evenly distributedstations in the city. Cross validation R2 is between 0.76-0.97, the most are greater than 0.90.

The related research results have been published in the PLoS ONE (Wang JF, Hu MG, Xu CD, Christakos G, Zhao Y. 2013. Estimation of citywide air pollution in Beijing. PLoS ONE 8 (1): e53400).

Software downloadable:http://www.sssampling.org/spa

For more information, contact

Professor WANG Jinfeng

State Key Laboratory of Resources and Environmental Information System

Institute of Geographic Sciences and Natural Resources Research

Chinese Academy of Sciences

A11, Datun Road

Beijing 100101, China