All web sites should have a site map, no matter how simple they are. Regular internet users have come to expect a clearly noticeable link where they can easily see everything a site has to offer with an easy way of navigating to what they're looking for. If a user can't find what they're looking for almost instantly, they'll just go to another site where they can find the information.
A link to your site map should be above the fold, an old newspaper term meaning when the paper is folded the text is visible on the top folded half. This applies to web pages translating to viewable in the browser window without the user scrolling down.
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