Graphics Reference
In-Depth Information
Figure
.
.
A smooth surface representing an estimate of the regression function of catch score on
latitude and longitude simultaneously
A clear drop in mean catch score as longitude increases is indicated. However,
more detailed insight is available fromthe estimated surface, with clear indication of
a nonlinear pattern with increasing longitude. In fact, due to the orientation of the
coast in this region, longitude broadly corresponds to distance offshore, leading to
anatural biological interpretation, with relatively constant levelsof marine life abun-
dance near the coast followed by rapid decline in deeper water. he smooth surface
therefore provides a significant enhancement of the display by drawing attention to
features of some potential importance which are not immediately obvious from plots
of the raw data.
It is natural to revisit in the setting of two covariates the discussion of the benefits
of adding further information, particularly on variability and reference models, to
displays of nonparametric estimates. he graphical issues are now rather different,
given the very different ways in which the estimate itself must be represented. One
possibility is to mix the different types of representation (colour, contours, three-
dimensional surfaces) with an estimate represented in one way and information on
variability in another. For example, the colour and contour displays in Fig.
.
might
be used for these two different purposes, although this particular combination can
be rather di
cult to interpret.
One attractive option is to combine surface and colour information and Fig.
.
illustrates this by painting the estimated regression surface to indicate the variations
in standard error in different locations. Discrete levels of colour have been used for
simplicity, with a separate colour associated with each individual polygonal surface
