The Mexican group adheres to some set criteria, requiring minimum population of 300,000 people and excluding places with active conflicts, like Ukraine or Syria.
But, the group says in its methodology, whenever possible it includes all the municipalities that it assess as part of a city — "localities that form a unique urban system, clearly distinguishable from others, independent of the geographic-administrative divisions inside the countries."
Muggah and his colleagues noted issues with this method in relation to the 2015 ranking, which found Caracas to be the most violent city in the world. That year, others also noted the group based its tally on the homicide total for the metropolitan area of Cali, in southwest Colombia, and, in their view, overstated the number of homicides.
The group's ranking for 2018, its most recent, put Tijuana at the top of the list, with a homicide rate of 138.26 per 100,000.
Tijuana has seen a precipitous rise in deadly violence, but the city's public-security secretary disputed its rank, citing the inclusion of the nearby city of Rosarito in the homicide count and the failure to account for Tijuana's migrant population.
SJP, for its part, rejected the criticism, saying that it based its population count on official numbers and that excluding Rosarito would have actually raised the homicide rate. (Though it did not say why it assessed Tijuana's metropolitan area and not that of other cities.)