The Sitemaps protocol allows a webmaster to inform search engines about URLs on a website that are available for crawling. A Sitemap is an XML file that lists the URLs for a site. It allows webmasters to include additional information about each URL: when it was last updated, how often it changes, and how important it is in relation to other URLs of the site. This allows search engines to crawl the site more efficiently and to find URLs that may be isolated from the rest of the site's content. The Sitemaps protocol is a URL inclusion protocol and complements robots.txt, a URL exclusion protocol.
Google first introduce Sitemaps 0.84 in June 2005 so web developers could publish lists of links from across their sites. Google, Yahoo! and Microsoft announce in November 2006. The schema version was changed to "Sitemap 0.90", but no other changes were made.
In April 2007 for Sitemaps. Also, Google, Yahoo, MSN announced auto-discovery for sitemaps through robots.txt. In May 2007, the state governments o Arizona, California, Utah and Virginia announced they would use Sitemaps on their web sites.
The Sitemaps protocol is based on ideas from "Crawler-friendly Web Servers," with improvements including auto-discovery through robots.txt and the ability to specify the priority and change frequency of pages.
Sitemaps are particularly beneficial on websites where:
* Some areas of the website are not available through the browsable interface
* Webmasters use rich Ajax, Silverlight, or Flash content that is not normally processed by search engines.
* The site is very large and there is a chance for the web crawlers to overlook some of the new or recently updated content
* When websites have a huge number of pages that are isolated or not well linked together, or
* When a website has few external links
The Sitemap Protocol format consists of XML tags. The file itself must be UTF-8 encoded. Sitemaps can also be just a plain text list of URLs. They can also be compressed in .gz format.
A sample Sitemap that contains just one URL and uses all optional tags is shown below.
The Sitemap XML protocol is also extended to provide a way of listing multiple Sitemaps in a 'Sitemap index' file. The maximum Sitemap size of 50 MiB or 50,000 URLs means this is necessary for large sites.
An example of Sitemap index referencing one separate sitemap follows.
The definitions for the elements are shown below:
Support for the elements that are not required can vary from one search engine to another.
The Sitemaps protocol allows the Sitemap to be a simple list of URLs in a text file. The file specifications of XML Sitemaps apply to text Sitemaps as well; the file must be UTF-8 encoded, and cannot be more than 50MB (uncompressed) or contain more than 50,000 URLs. Sitemaps that exceed these limits should be broken up into multiple sitemaps with a sitemap index file (a file that points to multiple sitemaps).
A syndication feed is a permitted method of submitting URLs to crawlers; this is advised mainly for sites that already have syndication feeds. One stated drawback is this method might only provide crawlers with more recently created URLs, but other URLs can still be discovered during normal crawling.
It can be beneficial to have a syndication feed as a delta update (containing only the newest content) to supplement a complete sitemap.
Search engine submission
If Sitemaps are submitted directly to a search engine (pinged), it will return status information and any processing errors. The details involved with submission will vary with the different search engines. The location of the sitemap can also be included in the robots.txt file by adding the following line:
The <sitemap_location> should be the complete URL to the sitemap, such as:
This directive is independent of the user-agent line, so it doesn't matter where it is placed in the file. If the website has several sitemaps, multiple "Sitemap:" records may be included in robots.txt, or the URL can simply point to the main sitemap index file.
The following table lists the sitemap submission URLs for several major search engines:
Sitemap URLs submitted using the sitemap submission URLs need to be URL-encoded, for example: replacing : (colon) with %3A, / (slash) with %2F.
Limitations for search engine indexing
Sitemaps supplement and do not replace the existing crawl-based mechanisms that search engines already use to discover URLs. Using this protocol does not guarantee that web pages will be included in search indexes, nor does it influence the way that pages are ranked in search results. Specific examples are provided below.
* Google - Webmaster Support on Sitemaps: "Using a sitemap doesn't guarantee that all the items in your sitemap will be crawled and indexed, as Google processes rely on complex algorithms to schedule crawling. However, in most cases, your site will benefit from having a sitemap, and you'll never be penalized for having one."
* Bing - Bing uses the standard sitemaps.org protocol and is very similar to the one mentioned below.
* Yahoo - After the search deal commenced between Yahoo! Inc. and Microsoft, Yahoo! Site Explorer has merged wit Bing Webmaster Tools
Sitemap files have a limit of 50,000 URLs and 50MB per sitemap. Sitemaps can be compressed using gzip, reducing bandwidth consumption. Multiple sitemap files are supported, with a Sitemap index file serving as an entry point. Sitemap index files may not list more than 50,000 Sitemaps and must be no larger than 50MiB (52,428,800 bytes) and can be compressed. You can have more than one Sitemap index file.
As with all XML files, any data values (including URLs) must use entity escape codes for the characters ampersand (&), single quote ('), double quote ("), less than (<), and greater than (>).
Best practice for optimising a sitemap index for search engine crawlability is to ensure the index refers only to sitemaps as opposed to other sitemap indexes. Nesting a sitemap index within a sitemap index is invalid according to Google.
Additional sitemap types
A number of additional XML sitemap types outside of the scope of the Sitemaps protocol are supported by Google to allow webmasters to provide additional data on the content of their websites. Video and image sitemaps are intended to improve the capability of websites to rank in image and video searches.
Video sitemaps indicate data related to embedding and autoplaying, preferred thumbnails to show in search results, publication date, video duration, and other metadata. Video sitemaps are also used to allow search engines to index videos that are embedded on a website, but that are hosted externally, such as on Vimeo or YouTube.
Image sitemaps are used to indicate image metadata, such as licensing information, geographic location, and an image's caption.
Google News Sitemaps
Google supports a Google News sitemap type for facilitating quick indexing of time-sensitive news subjects.
Multilingual and multinational sitemaps
In December 2011, Google announced the annotations for sites that want to target users in many languages and, optionally, countries. A few months later Google announced, on their official blog, that they are adding support for specifying the rel="alternate" and hreflang annotations in Sitemaps. Instead of the (until then only option) HTML link elements the Sitemaps option offered many advantages which included a smaller page size and easier deployment for some websites.
One example of the multilingual sitemap would be as follows:
If for example we have a site that targets English language users through http://www.example.com/en and Greek language users through http://www.example.com/gr, up until then the only option was to add the hreflang annotation either in the HTTP header or as HTML elements on both URLs like this
But now, one can alternatively use the following equivalent markup in Sitemaps: