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.
Sim Superclusters are more then 50 sims wide (12.8 km) and sometimes they host more then 100 sims.
Mathematic Sim Clusters are sim clusters where sims are placed in a mathematic order. Usually, there are two main models of mathematical sim clusters: Square Clusters orisontal and vertical, leaving void channels between them that look like American streets on a city map (between one and 5 sims wide) and Diagonal Clusters, where sims are placed in diagonal, having contact one to another only at the corners.
The fall 2013 census found 91 sim clusters. 7 of them surround a microcontinent and one surrounds Estate Continent.