Pagerank , backlinks , content all terms matter in crawling process. For crawl , google has decide some algorithm. And in crawling it decide that how much time it crawl the site , and how pages be cached in crawling process and more. You can more read from google webmaster help centre.
Crawling process is also a spidering.use It provide up-to-date data. It mainly used to create a copy of all the visited pages for later processing by a search engine.It help index our website.
Crawling is simply Googles (and other search engines) way of indexing your page. They will record the textual content of the page aswell as relevant tags such as titles, meta, headings, etc. The bot will then follow links to other pages of your website until it can find no new pages to go to. As prcys said already, Google webmaster tools has a crawling section which shows you how often Google crawls your website and even allows you to specify your preferred crawling speed and delay between crawls in Site Config > Settings. if you want to see how Googlebot (Googles crawler/spider) sees your page you can click on Diagnositcs > Fetch as Googlebot The resulting text and tag data from your crawled page is then combined with link analysis and many other factors that Google use in their Algo to decide the keyword relevancy and importance of your website and pages.
Crawling process is also known as Web crawling or spidering. Many sites, in particular search engines, use spidering as a means of providing up-to-date data.
Rank, background, and content of each issue of terminology in the process of crawling. For crawl, Google may decide some of the algorithm. It was decided that how much time you crawl crawl thesite, and how to be temporarily in the process of crawling pagesand more. You can read more from the Google Help Center is responsible for the site.
Crawling process- Crawling process is algorithmic. Google see the site Structure and Content, keywords , h1 & h2 tags, image tag, alt tag, Meta tags and etc.