Local smoothing of scatterplots
Lowess can be used to smooth time series but was originally developed as a general way to draw a smooth curve on any type of scatterplot. Again, the smoothed value for any observation is obtained by fitting a least squares line to the observations with adjacent values for the explanatory variable. The fitted values that are obtained in this way are joined with lines.
(Most computer software implements a version of lowess that is a actually bit more complex than has been described here but our simpler version gives a good flavour of the method.)
Rose powdery mildew