I would hypothesize it&#x27;s because smell is &quot;Sparse&quot;. I believe we have so many receptors with such specificity that it&#x27;s less useful to think in terms of &quot;dense&quot; parameters. In comparisson with other senses, for music we can locate a sound in a pitch spectrum since we have many receptors (millions?) with sensitivity across a single dimension (frequency). For color, we have just three receptors, lending perceived elements to be put in a nice three dimensional space. Now with smells, we have so many different and so specific receptors that there&#x27;s neither a canonical order for the receptors to be put across a dimension (the case with sound) or a dense set within a few dimensions (vision, taste). So we just associate each receptor with the most common source.