Having recently gone through a site merge/migration, it's been quite an enlightening experience for me. Moving one website to another is one thing, but merging multiple websites into one, is a different story entirely. Here are some tips which came in handy for the merger and migration.
Benchmarking First things first, always have a benchmark so you have an idea of where you're coming from. This could include the online visibility or current ranking positions for key terms of all the websites individually, prior to the site merge. Something else you might want to consider is the traffic statistics and trends of all the websites individually. Once the merger is completed one can fall back on the benchmark to see if there been an success with the merger or not. Website crawling Next step, crawl all the pages of the website to be merged. With this, we'll get a list of all the available pages within the websites. One of the easier ways of doing this is to use a site crawler like Xenu Link Sleuth. This would give you a list of the pages and possibly broken pages as well. This would also be a good time to do some cleaning up and fixing all broken pages on the website. Once you've complied the list of active and broken pages we can move on to making good use of this list. Mapping webpages Once we have a list of all webpages from the sites to be merged and an equivalent list of pages for the new websites, we can start mapping pages. This involves mapping one webpage to another based on its relevance. For instance, all contact pages should be mapped to the new contact page. If there isn't an exact page to be mapped to, it is worth considering if a new page should be created or not. This needs to be done systematically to avoid any broken 404 pages and wrong mappings. Setting 301 Redirects After the webpage mapping has been completed for all the websites we need to create 301 redirect rules. Using the mapping document we setup rules to point one page to another. Setting up the redirection rules depends on what server is being used - Microsoft or Apache - either way, the redirection code needs to be setup and put in place in preparation for the site migration. Setup Google Webmaster Tool This should be one of the tools used to monitor the progression of the site migration when it's finally set in motion. GWT should be used to submit a sitemap.xml page to give Google crawlers access to all the webpages found on the newly merged website. It's also a handy tool to check for missing webpages which are being linked to internally and externally. Crosschecking Redirects When the site merge has been completed, it's a good idea to cross check that all the old pages are actively being redirected to the right page. If a redirect has not be setup or is broken this can be highlighted and updated accordingly. Site migration can be pretty straight forward or a complete nightmare, it all depends on how it is approached. One of the most important things to take away when doing a site migration is to plan and plan some more, then take it systemically to avoid errors. All in all, it should be quite straightforward especially with these tips.