Hot answers tagged layers
If you're writing a geoprocessing script, I'd recommend authoring a .lyr file you bundle with your toolbox and set the symbology in the script tool parameters to point to the .lyr file (see the "Symbology" part of the dialog).
You need to use Vector->GeoprocessingTools->Dissolve and dissolve by an attribute (Dissolve Field) to merge subdivided polygons.
You can show as many categories as you want in one layer, but you'll have to do some custom coding. My approach would be: Start with as many categories as you can using the Category Visualization Wizard (which I assume you're already doing). Click the CSS icon on the sidebar. This takes you to the CartoCSS editor. Here you can copy and modify the style ...
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