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In Metview 4, the default behaviour is to always overlay fields from different sources, even if their meta-data, such as date/time, do not match. This is different from Metview 3, whose default behaviour was to only overlay data whose timestamps 'match'. In Metview 3, there was a separate icon, the Overlay Control icon, which could be dropped into a View icon to change the overlay settings. In Metview 4 this is simpler, with a Map Overlay Control parameter directly in the Geographical View icon. See Data Overlay for more information.
Layer Ordering and Drawing Priority
Metview 3 used the Drawing Priority rules to determine which layers appeared on top of others (e.g. wind flags on top of shaded contouring). This was true even in the Macro plot() command, so that the order in which the layers were specified was not necessarily the order in which they were drawn. In Metview 4, the intention is that the plot() command honours the order in which the layers are specified, ignoring the old Drawing Priority rules - the first data layer supplied will appear as the bottom layer of the plot, etc. This is the case when using the new visdefs such as mcont and mwind, but when using the old ones such as pcont and pwind, the old Drawing Priority rules are applied as they were in Metview 3, allowing some backwards compatibility. This separation of behaviour breaks down when old and new visdefs are mixed in a single plot() command, e.g. plot(t_data, pcont_def, wind_data, mwind_def). In this case, the two behaviours clash and the results might not be as desired. It is best to convert old visdefs to their new equivalents, and use the order in which they appear in the plot() command to determine the order in which they are rendered.
Cross Section Data, Average Data, Hovmoeller Data
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