My question is how best to decide which layer (from a set of nested, aggregated census polygons) to display for any given map extent in an online map.

Australia's census boundaries are built from multiple layers, aggregated from highly detailed collection districts through a number of intermediate layers to eventually comprise the whole country. This same principle applies to city/county/state/country boundaries.

Switching census layers based on scale dependency is unsatisfactory, since there must be a compromise between the populated cities and the vastly empty interior. Eg, over Sydney the Collection Districts should show at around 1:10k whereas in rural areas they should show above 1:500k

1) Are there any examples available in online maps where this problem has been solved elegantly? All of the examples I've seen use scale dependencies to switch layers on/off

2) I'm contemplating counting the features every time the map extent changes, and using this to decide which is the best layer to display. This "breaks" the traditional GIS paradigm whereby layers can switch on/off based on scale, since in my scenario they may also switch on/off based on different map extents at the same scale.

Are there any examples of this in action? Does anyone have any thoughts or advice on whether this will be confusing to the user?

Eg, a user might be viewing Collection Districts, then pan the map slightly. This could cause the Collection Districts to switch off, and the next layer to switch on. Has this been done anywhere before?

Thanks,
Steve