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You could stick to the 12 directories you currently have on your website.

How about one directory for Las Vegas and another for the rest of Nevada?

Or, using the Campiglia/Wells Guide, have directories for Las Vegas, Lake Tahoe, Reno, Small Towns (All other)

Another option would be to check with Terry Shaffer. It may be possible to incorporate what you have into his database, which could then be uploaded to your website. Might just be possible. Good luck!

Just my one and a half cents...