Recently, MAUP has been intensively addressed by researchers, some of whom sought to identify some effects of MAUP on statistical results, and others tried to edify the problems. Obviously, soaring attention paid to MAUP is associated with recent findings and technical advances in spatial statistics, which basically aims at spatializing the general statistics. The main purposes of the paper were: (1) to review and compare major functional regions generated by aggregating counties in the US especially in terms of different schemes of spatial aggregation; (2) to calibrate some effects of MAUP across the functional regions by reference to general findings derived mainly from simulation approaches. The major findings of the research can be summarized by several points: (1) the thesis of increase in variances and correlation coefficients in accordance with upward spatial aggregation generating less and less spatial units was evidenced by our data sets; (2) the thesis of increase in regression coefficients and coefficients of determination was hardly supported by the data sets; MAUP seemed to be variable-specific; (3) the relationships between Moran`s I and levels of spatial aggregation did not appear generalizable. Some explanations on the discrepancies between generally accepted findings about the effects of MAUP and those from the real data sets used for the research might be given by the fact that a functional region is not just one instance of enormous number of spatial aggregates possibly derived from base units. Rather, it is a thoughtfully designed spatial unit which could provide researchers with a much more reliable and sounder basis than the base unit could do. Moreover, in order for the research on MAUP to further itself, it should be able to help evaluate dependabilities among different regionalization schemes for the functional region.