Dataset defined discontinuites, where the clusters have different variances.
Three main Clusters, and four Outliers (in Cluster 4). See for a more detailed description in [Thrun, 2018].
References
[Thrun, 2018] Thrun, M. C.: Projection Based Clustering through Self-Organization and Swarm Intelligence, doctoral dissertation 2017, Springer, Heidelberg, ISBN: 978-3-658-20539-3, https://doi.org/10.1007/978-3-658-20540-9, 2018.