444: CCA Maps

The CCA maps (or bar charts if the data are unreferenced) show similar results to the Loadings and Scores , but show the weights for the X and Y components of the CCA modes together. The corresponding temporal scores on the centre graph (the red line is for the X variables, and the green line is for the Y variables). It is the correlation between the curves shown on this central graph that CCA attempts to maximise. The canonical correlation is a function partly of any relationships between the X and Y data that CPT exploits to make predictions, but also partly a function of the numbers of X modes retained. Thus, the canonical correlation can be artificially inflated simply by forcing CPT to retain a large number of modes. High canonical correlations should not necessarily be interpreted as a sign of a good predictive model.

The weights and scores for different CCA modes can be displayed using the control at the top left of the CCA maps window, but, unlike the X and Y modes , only those CCA modes that CPT retains can be viewed. The results can be saved to an output file from the CCA Results tab in File ~ Output Results , but the actual weights are saved rather than the correlations between the original gridded / station / index data and the temporal scores for the corresponding X and Y components of the CCA modes.

The map and graph titles can be set using the Customise option upon right-clicking in the child window. There is some flexibility to adjust the colour scaling on the maps: the colour bar limits can be set by right-clicking on the image and then selecting the Customise ~ Contour Limits option. A window opens that indicates the assumed maximum and minimum data values when setting the colour intervals and number of colours. These values can be reset, which will in turn automatically reset the colour interval and number of colours. Similarly, the y-axis limits on the graph can be set by right-clicking on the image and then selecting the Customise ~ Y-Axis Limits option. Resetting these axis limits will in turn automatically reset the tick-mark interval and number of tick marks. Greater flexibility for setting the colour scaling and tick marks is planned for future releases. Further options for customising the maps and graphs are available from Options ~ Graphics .

The maps and graphs can be saved as graphics files, individually or as a montage, by right-clicking anywhere in the child window and selecting Export from the pop-up menu. A default name is given to the graphics file, but this name can be changed using the browse button. The image quality for all the graphics formats can be improved by increasing the size of the image (see Options ~ Graphics ~ Graph Scaling ).