Hi, I have a large website that I'm creating an XML sitemap for. I want to try to make it easier for the search engines to crawl pages, but at the same time I'd like to know how many pages in each category/'url directory' are indexed. GWT tells me how many URLs in each sitemap are indexed so I thought that uploading multiple sitemaps would be a helpful way to achieve this.

What I'm wondering is, is there a XML sitemap generator out there that will create 1 sitemap per 'url directory' and automatically keep those sitemaps up to date and ping the SEs when updated?

I have an Apache server and I using PHP.