How to have many pages indexed

Why is it necessary to have many pages indexed in Google? For example, let's say you have the domain www.catland.com and you have an article on ‘Cats’ at www.catland.com/cats/articles/cats.html

In order to get to this article you have to click “Cats” on the homepage and then 'Articles on the following page. On this cats page, you have your meta tags, evenly distributed content, and all of the hints from the Optimization articles.
But what most people miss out on is that this is all useless if your articles page is not indexed in Google. 

Search spiders that crawl your website on average only crawl into your website one or two levels deep.  In order to have your Articles page indexed so that your webpage comes up as a result in a search engine for “Cat Article”, you need a site map.

A site map is basically a webpage that has ALL of the links you would like listed in Search Engines. Ideally, this should be done on the homepage; but if you go one level deep into your webpage, that should be ok as well.

For example, lets consider having a sitemap with the URL ‘sitemap.htm’. On the Homepage, we link to this sitemap.

Sitemap.htm would contain links to all of the html files for example, the Sitemap for my Cat website would look something like:

<a href=”www.catland/index.htm”>Cats Article</a>
<a href=”www.catland/cats/articles/article1.htm ”>Cat Food Article</a>
<a href=”www.catland/cats/articles/article2.htm ”>Cat Vitamins</a>
<a href=”www.catland/cats/articles/article3.htm ”>Cat Sleeping Pills</a>

By doing this, a search engine will have record of all of your website’s pages just by crawling sitemap.htm and more of your webpages will be indexed in search engines!