Plots are contained in a plots collection, which in turn is contained in a site.
A drawing can include any number of sites, but each site has only one plots collection. No unique plot can belong to more than one site. You can see these relationships in the Sites collection in Toolspace, on the Prospector tab:
Plots in a collection can be either unattached or touching, but they cannot overlap. If you attempt to overlap two plots, the region of overlap defines a third plot. Similarly, if an alignment crosses a plot, it divides the plot into two plots. In the following illustration, before adding the alignment, the site was all one plot:
In situations that require overlapping plots, such as overlaying a subdivision with soil regions, you can put the subdivision plots in one site and the soil region plots in another site. Multiple sites can overlay one another because their topologies are independent. Although everything within a site is topologically related, sites are not topologically related to each other.