Scope of listing

Most of the directories are general in scope and list websites across a wide range of categories, regions and languages. But some niche directories focus on restricted regions, single languages, or specialist sectors. One type of niche directory with a large number of sites in existence is the shopping directory. Shopping directories specialize in the listing of retail e-commerce sites.
Examples of well known general web directories are Yahoo! Directory and the Open Directory Project (ODP). ODP is significant due to its extensive categorization and large number of listings and its free availability for use by other directories and search engines.[5]
However, a debate over the quality of directories and databases still continues, as search engines use ODP's content without real integration, and some experiment using clustering. There have been many attempts to make directory development easier, such as using automated submission of related links by script, or any number of available PHP portals and programs. Recently, social software techniques have spawned new efforts of categorization, with Amazon.com adding tagging to their product pages.
Directories have various features in listing, often depend upon the price paid for inclusion:
Free submission – there is no charge for the review and listing of the site
Reciprocal link – a link back to the directory must be added somewhere on the submitted site in order to get listed in the directory
No Reciprocal link — a web directory where you will submit your links for free and no need to add link back to your website.
Paid submission – a one-time or recurring fee is charged for reviewing/listing the submitted link
No follow – there is a rel="nofollow" attribute associated with the link, meaning search engines will give no weight to the link.
Featured listing – the link is given a premium position in a category (or multiple categories) or other sections of the directory, such as the homepage. Sometimes called sponsored listing.
Bid for position – where sites are ordered based on bids
Affiliate links – where the directory earns commission for referred customers from the listed websites