A sim cluster is a group of many sims (more then 10) that are connected only on diagonal (and can belong to different estates). Also a sim cluster is a group of sims that are close one to another, but not in direct contact and belong to the same estate. Sometimes, a sim cluster can have more then 30 sims, that is the minimum limit for a continent, but they are not a continent since their sims are not connected.
Sim clusters are the most common feature we see on the map. Sometimes their architecture is the result of random combination, sometimes behind this there is the work of an estate manager. It is impossible to count all the sim clusters, however there should be hundreds or thousends.
The Estate Continent is composed of a central continental mass and is close to a sim cluster.