A SiteA structural element of a Maximo database that is used for data separation. More may represent a single physical site where assets exist. A Site may be a whole territory, or country where there are many physical locationsA physical place where assets exist and where work can be performed. More where assets exist. Locations, Assets, Storerooms and Work Orders all exist at the site level in Maximo. You cannot link locations to other locations that belong to different sites, you cannot have an asset hierarchy where the assets exist in different sites, all the work order in a work hierarchy must belong to the same site and the work can only be performed on the assets and locations in the same site. 

I like to think of sites like islands. The assets and locations exist on the island and work is performed on the island’s assets, but there are no bridges or tunnels between the islands. A person (labor) may perform work on assets that are on multiple islands, but those work orders cannot be joined together into a work package of work orders.

The Site object is a System level object, the key field for a Site is SITEID. Site identifiers are unique across the whole Maximo database; therefore, it is normally quite wrong to reference the organization identifier (ORGID) as well, you would be asking the database to perform an extra step to verify the organization, which it need not do. You cannot change the identifier of a site, therefore take time in deciding this.