This paper identifies five phonetic characteristics (seseo, yeismo, /s/-aspiration, rehilamiento, and /x/-aspiration) whose presence or absence allows to distinguish among ten regional varieties in which the entire universe of Spanish speakers can be divided. We also show that, in order to phonetically transcribe a text, taking into account those distinguishing characteristics, it is enough to use 27 phonetic symbols, that constitute an extended phonological inventory that includes both the "controversial" and the "non-controversial" Spanish phonemes.
Coloma, G. (2011). Caracterización fonética de las variedades regionales del español y propuesta de transcripción simplificada. Revista de Filologia Romanica, 28, 11–27. https://doi.org/10.5209/rev_rfrm.2011.v28.37217