1. A method for hierarchical visualization of multi-dimensional data, comprising: (a) applying a first dimension-reduction process to a multi-dimensional data set to obtain a first visualization; (b) selecting a subset of the multi-dimensional data set associated with a selected region of the dimension-reduced first visualization where more detail is desired; and (c) applying a second dimension-reduction process to the selected subset of the multi-dimensional data set to obtain at least one additional visualization.