OCPN does not quilt raster charts (KAPs) with vector charts other than cm93. And it never has.
Why and/or how can we quilt with cm93 so readily? Because we know that cm93 is continuous worldwide (except high latitude). So we simply add in cm93 wherever there is nothing else to show except the lo-res backing chart.
Should O quilt rasters and vectors together? Well, maybe....
One can always find specific geolocations and chart cell availability to wish that O would "do the right thing" in this instance. The right thing being what you want it to do, logically.
But actual live coding logic for the cases of arbitrary chart availability, display scale, and location is not trivial in practice. I suppose one could develop some display policies, or profiles, from which a user might select.
a. No mixed quilt
b. Mixed quilt, giving preference to raster for equal scales.
c. Mixed quilt, giving preference to vectors for equal scales.
d. Mixed quilt, unless available cm93 cell is larger scale than vector/raster target.
e. Mixed quilt, giving preference to most recently updated chart of whatever family
f. etc, etc.
Quilting needs to play nice with the ChartBar as well. The original idea of the ChartBar, individual chart disable options, and scale in/out buttons was this:
Faced with a navigation
task, and looking at a chart drawer full of "virtual" charts, the navigator is in a better position to decide what chart to reach for than digital logic ever could be. So we have these controls to override the predictable internal logic of OCPN.
I hope this discussion makes sense. Clearly there will be no major change in O's quilting logic for O4.2.
But I would like to continue exploring ideas here in planning for (dare I say it?) OCPN V5, coming in 2016.