Good or Bad? Google's Specialized XML Sitemaps Combined Into One
In the simplest of terms, XML Sitemaps are lists of the pages / files on your Website. They allow you to send Google a direct list of all the pages / files on your Website, including those pages that may not normally be found via Google's search crawlers. Keep in mind that just because you have all your Website's URLs listed in the XML Sitemap doesn't mean Google WILL crawl or index all of them.
In addition to your typical XML Sitemap, Google also supports the following specialized XML Sitemaps: mobile, video, images, code search, geo and news. Until recently, Webmasters had to create separate XML Sitemaps for each of the specialized formats. Now, you can combine all of your specialized XML Sitemaps into your main XML Sitemap; combine multiple XML Sitemaps down to one. Yeah! Well maybe?
For some webmasters this may be a huge plus, however there are advantages to keeping your XML Sitemaps separated:
Metrics: By submitting individual XML Sitemaps for various media types as well as your most important content you can measure indexing, links, etc on a more direct level. For example, when you submit an XML Sitemap to your Google Webmaster Tools account, you can see the # of URLs submitted as well as the # of URLs indexed. By having a separate images XML Sitemap you can narrow that count down further to knowing how many of your Images Google is indexing versus them being lumped in with Web pages.
Size Limitations: With the new change, Google has NOT increased the current limits on the number of URLS and size that can be included (50,000 URLs and 10MB), so if you are a large Website with many media files, you will still need to use multiple XML Sitemaps.
Alliance: How does this change affect the Sitemaps.org Alliance (2006) between Google, Yahoo and Bing? The Alliance created a uniform support for the Web page XML Sitemap format; however Google launched specialized XML Sitemaps on their own. Yahoo and Bing do not appear to support the specialized XML formats. The question is then raised that isn't Google working against the Alliance by combining the specialized XML formats into one XML Sitemap without the input of Yahoo and Bing on the matter? If you create one main XML Sitemap with all the specialized attributes included, will Bing and Yahoo be able to understand it? That's the big question now isn’t it? Maybe it is not a big deal, but wasn't the purpose of the Alliance to make things easier for the Web site owners? Seems to me Google may have done the opposite.