While I'd expect people to answer this question by saying 'depends on the distribution of data', but what are the thumb rules for deciding which grid to use (either hexagonal or rectangular) for generating a SOM?
For rectangular grid there are a few heuristic rules to choose the grid dimensions and number of neurons, but I couldn't find anything on a hexagonal grid. So how do I begin with and what preliminary observations to take in consideration to choose the size?
Also, when using
kohonen package in R to build a SOM, the default settings of the
som() function are to use a circular neighbourhood for hexagonal grid, and square neighbourhood for rectangular grid.
Is there a reason for such default values? In many examples available online, a rectangular grid has been used with a circular neighbourhood.