The answer to that question is pretty simple in our opinion. Yes you can have more than one Sitemap. What you need to have is an index Sitemap that links to the other Sitemaps. What you’ll then need to do is submit that index Sitemap to the search engines. The standard protocol on this subject is set out on http://www.sitemaps.org/protocol.html
Any website can provide multiple Sitemap files, but each Sitemap file provided can’t have more than 50,000 URLs and mustn’t be larger than 10,485,760 bytes (10 MB). You can compress your Sitemap files using gzip to reduce your bandwidth requirement; however the Sitemap file once uncompressed must still be no larger than 10MB. If you want to list more than 50,000 URLs, you must create multiple Sitemap files.
If you do provide multiple Sitemaps, you should then list each Sitemap file in a Sitemap index file. Sitemap index files can’t list more than 50,000 Sitemaps and can’t be larger than 10MB. They can, however, be compressed. You can have more than one Sitemap index file. The XML format of a Sitemap index file is similar to the XML format of a Sitemap file:
- It must begin with an opening <sitemapindex> tag and end with a closing </sitemapindex> tag.
- It must include a <sitemap> entry for each Sitemap as a parent XML tag.
- It must include a <loc> child entry for each <sitemap> parent tag.
(The optional <lastmod> tag is also available for Sitemap index files)
It should be noted that a Sitemap index file can only specify Sitemaps that are found on the same site as the Sitemap index file, and that a Sitemap index file must be UTF-8 encoded. Sitemap URLs, like all values in your XML files, must also be entity-escaped.
Having multiple Sitemaps that link back to an index Sitemap is acceptable as long as long as all URLs listed in the Sitemap are at the same location as the Sitemap or in a sub directory. What is important is that Sitemaps does not contain URLs from parent directories or completely different directories. If this occurs Google can’t be sure that the submitter controls the URL’s directory, so it can’t trust the metadata. For further information see http://googlewebmastercentral.blogspot.co.uk/2006/10/multiple-sitemaps-in-same-directory.html