Unassociated sims are large groups of sims that cannot be grouped into a continent, microcontinent or sim cluster. They have an average sim density and the sims that form them are not disposed into a Geometrical pattern (square, diagonal, lines). These kind of structures form the space between sim clusters or microcontinents. They are a common feature of all Second Life oceans. An estimation is that the unassociated sims are about 30% of the total private-owned sims.
It is impossible to make a map or a list of unassociated sims. Also, it is very difficult to group these structures.
Some unassociated sims are a result of degradation of a former sim cluster or microcontinent. This process is common when an estate is running out of money and needs to abandon part of its sims. Some of them are formed another way, by creation, deletion and movement of sims.
Unassociated sims may belong to larger estates that own microcontinents and sim clusters, but usually they are owned by small estates that own only one or a few sims. This is why they offer the highest variety. It is possible that near a dark vampire sim to find a large park with flowers and near an oasis of recreation to discover an adult erotic place.
Also, unassociated sims offer the highest diversity of Geographical features, that includes mountains, hills, plains, plateaus, submerged land, tunnels, caves, skyboxes and any possible thing. Vegetation varies up to unpredictable limits.
Unassociated sims are different from other structures on map. Private Land Geography Research shows important differences in percentage. For example, Gorean Sims are found more often, while the tropical beach paradise is more rare then on grouped map structures.
It is impossible to group all unassociated sims. Small grouping can be done into sim groups or sim cousters, but their borders are not clear and everybody might fix other borders. However, unassociated sims are a lot more frequent in some parts of the grid and cannot be found in other parts. See Oceans (and the links to each ocean) for more info.
They are 30% of all private-owned sims, that means about 6000 sims. This is comparable to all Linden-owned land. At such a great number, they should be treated with respect, but it will never be possible to make a complete article about them. Additional data can be obtained from Gridsurvey. Gridsurvey has information about all existing sims and even for vanished sims, including Coordinates that can help find the current position of that sim. From there, you can see pictuers token on almost every sim on Snapzilla (sometimes even from places with restricted access and also with useful information). Another useful link is SLuniverse.