I would definitely provide "normal" or regular "a href" links to the pages so that the spiders can crawl the site. But, keep in mind that using zip codes or another type of geography might not be appropriate for the site.

You need to think of your users first, and how they would typically look for the site to be categorized. If they would be concerned in finding a listing near them, then using geography would make sense. But, if that's really not an issue (in some industries, the users are looking for the type of product or service and don't care where it's located), then you need to categorize it in some other way.

I would first make sure you are familiar with the "theme pyramid" type of internal linking. I would then use a breadcrumb trail to break it all out by categories.

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Bill Hartzer's Blog