Site Hierarchy in SharePoint 2010
SharePoint 2010 sites are organized into a hierarchy of containers. Some containers are sites that contain content, whereas other containers simply act as entry points into a group of sites. These containers map to web addresses, which is how you access them.
The highest level container in SharePoint is a Web application, which is usually used to logically group together content and users who have similar needs.
For example, say your organization consists of two different companies — Big Bagel Makers, Inc. and Big Donut Makers, Inc. The bagel makers and the donut makers have their own employees, business process, and content. What’s more is that never the two shall meet (Melvyn Einstein shouldn’t be sniffing around to learn how to make Homer Simpson’s favorite donut).
To meet these business requirements, your IT department can set up two separate web applications. Each web application can have its own web address. If you work for Big Bagel, use portal.bigbagel.com. Your cousin who works for Big Donut uses portal.bigdonut.com to access her content.
In this example, you know the web address of your portal based on where you work in this organization. If your organization consists of one company, you may only have a web application — mycompanyportal.com.
A web application provides an entry point into a site hierarchy and allows IT to configure policies that apply to every site within that web application. A web application contains a group of site collections, which contain content such as web pages, document libraries, and lists.
A site collection can also contain a hierarchy of sites, or subsites. A site collection may also consist of only one site — the root or top-level site.
Publishing sites have a Site Content and Structure tool (accessible from the Site Actions menu by selecting the Manage Content and Structure option) that you can use to view the site hierarchy within a site collection. This is a really cool tool because you can use it to move documents between libraries within the same site collection.
Many organizations use the site collection as their container of choice for creating new sites, which is clearly how Microsoft intended for site collections to be used. To state that another way, it’s usually better to create a new site collection than it is to create a new site within a site collection.