Hi Dan,
In fact our developer just handled the index build logic for Nautical Charts, you should want to try this version: https://www.nuget.org/packages/ThinkGeo.MapSuite.Layers.NauticalCharts/11.0.0-beta012
The speed get faster when build index, you can find more detail information from this topic: Nautical Chart Indexes
The index file will be used each time you get data from your data source, the index is help you quickly get necessary source, so when you refresh or pan or zoom, it is required.
And if your index file hadn’t built succeed, you can set “RequireIndex” equal false to shape file, then shape file will be rendered slower, but for NauticalChartsFeatureLayer you cannot do that, it looks the index file is necessary.
I think you should need build index for NauticalChartsLayer background, and after it is generated, you can tell user this layer is ready to be render.
Wish that’s helpful.
Regards,
Ethan