first order spatial variation

First order variation in a spatial pattern is that part of the pattern that may be attributed to trends across the study area. The most obvious example is a steady (say) south-north decrease in average temperatures across a region. The part of a pattern that is considered first order is likely to vary with spatial and temporal scale. Marked first order effects in a pattern can be problematic for some methods such as kriging, when universal kriging should be used to account for the first order effect. First order components in a spatial pattern may be effectively modeled using trend surface analysis. See also second order spatial variation.