# Dictionary:Trend analysis

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**1**. The fitting of an analytic surface (the **regional**) to data points as a representation of the ‘‘order’’ in the data, as opposed to the erratic element (the **residual**). The objective may be to analyze trends in the data or to interpolate between data points. The underlying assumption is that the data may be decomposed into a relatively low-order, smooth surface plus more-or-less random noise. The number of independent parameters in the analytic surface should be appreciably less than (usually less than 10 percent of) the number of data points. Also called **surface fitting. 2**. The 2D Fourier analysis of a surface into spatial frequency components (or wavelengths) so that one can determine preferred orientations and wavelengths.