Many people wrongly believe they cannot cater for accessibility and still optimize their websites for top placement in search engines. However, making your site accessible is about writing simple, valid, standards compliant code. It involves enabling users to access your site without using scripts or plug-ins and creating descriptions of images and transcripts of multimedia files. All of these things will also help search engine spiders access and understand your site.
When a search engine spider visits your site it looks at the source code of your page not the page itself. If you use simple code then the search engine has an easier time finding the content and important links on each page of your site. A webpage which makes sense when read in a linear fashion allows blind users to hear your page coherently. Using Cascading Style Sheets instead of tables helps you to design linear pages. In much the same way that getting rid of layout tables and switching to external CSS helps users of text-to-speech software and people surfing without a mouse, having less code for each page also helps the spider look deeper into each page by reducing what the spider has to read to understand each page. This enables you to structure your code using divs so the spider reads your content first and then your internal navigation before looking at external links or advertisements. Furthermore, adding headers and summaries to your data tables adds keyword-rich content to your pages that search engine spiders will find useful when categorising your website.
SEO experts will always tell you to write keyword-rich page titles and metatags. Using your metatags to tell search engine spiders what your page is about can also help users of text-to-speech software. Giving each page of your site a unique and descriptive title will tell both search engines and users where they are and what to expect on the page. However, you should never stuff your metatags with lists of keywords. The search engines consider that spam and blind users will have to listen to long titles read out. The more metadata you provide the better. Through use of the language tag the search engine then knows where to index your site and the screen reader knows how to pronounce the text on the page.
You should add descriptive alt text to any image or section of an image map that is important to the content of a page or the navigation of a site. Without alt text a search engine cannot tell the purpose of an image any more than a blind user. By putting concise alt text describing an image for every important image or graphical link you not only help your users but you add keyword-rich content to your pages for consumption by search engine spiders. This does not mean you should stuff keywords in your alt text but rather by properly describing the images on the page you add more information related to the subject of a page for the spider while also helping users of text browsers or screen readers better understand the content of your page.
Usethe clearest possible language on your website because it ensures your target audience can understand your content. If you choose the right words for your audience it means you are using the same language that your customers would choose when using a search engine. Half the battle in being found via a search engine is knowing which keywords to target. If you speak to your audience the way they speak themselves you are more likely to choose the best keywords.
A site map with a link on the main page of your site can help a search engine find every page on your site. If you use several tiers of navigation or dropdown menus without a site map a search engine spider may not reach the lower levels of your site. In the same way someone who has a cognitive disability - or is using a screen reader - may have trouble following your navigation. But if they find an alphabetical site map they can find what they need on your site.
Providing a text transcript to any multimedia on your site not only allows users with disabilities to access your multimedia material but it also makes the content available to search engine spiders. A search engine cannot see a flash movie nor can it hear an audio presentation. By providing a text version you enable the search engine to index the content on your site in full.
Clearly defined link targets are very important to the accessibility of your site. Very often a person using a screen reader will simply tab through the links on your site or call up a list of all the links. If you have links reading 'more' or 'click here' they will not know what information is contained on the target page. You should always describe where a link goes. For example: 'more about mobile phones' is better than 'more.'
When a search engine indexes a page it not only looks at the text on the page but at the link text pointing to that page. If someone links to a page of your site saying that page is about 'blue widgets' then the search engine assumes somewhere on that page is information related to 'blue widgets.' Your internal site links will also work in the same way. If you have a page about 'red widgets' then you want your links to contain these keywords - or synonyms for these words - to help the search engines learn to index your page. Using keyword-specific link text helps both user and search engine for exactly the same reason. Both parties will know the topic of the target page.
In conclusion, by making your site accessible to users with disabilities you also make it accessible to search engine spiders. Building a site which is universally accessible will mean taking care with certain aspects of your design. By titling each page, researching your keywords and link text and using the same language that your users use to describe your site you will also help search engines to better understand the subject of your pages and rank you for the most appropriate search terms. Paying attention to your site structure and providing accessible versions of multimedia will ensure that the search engine can find and index every page on your site and that users with disabilities can view all the important information they need.