An interactive map of drugs in Mexico

FORMALLY, power in Mexico is shared between 31 states and one federal district. Informally, it is also shared by eight large drug-trafficking organisations. These “cartels”, as the mobs are known (despite competing ruthlessly for market share, unlike real cartels), battle each other and the Mexican government for control of multi-billion dollar drug-trafficking routes to the United States. The cartels' territory, and the routes over which they squabble, have been mapped by Stratfor, an American security analysis company.

The latest update shows how scrappy the battle for territory has become. Whereas a few years ago Mexico's dope trade was carved up between five big outfits, those territorial distinctions have blurred. A push by the Mexican security forces has upset the pax narcotica that previously reigned, triggering a sickening rise in violence as gangs mark out territory with severed and skinned heads.

The past year has seen the continued rise of the Sinaloa cartel at the expense of mobs such as the Carrillo Fuentes Organisation (also known as the Juárez cartel). Government forces have dealt heavy blows to La Familia Michoacana, and forced the Beltrán Leyva cartel to split into rival factions, one of which was severely weakened by the subsequent arrest of its leader, Édgar Valdez Villareal. Yet the death toll has only risen: 2010's body count was nearly a third higher than that of 2009.

The map's most ominous feature is its southern edge. Mexico's cartels are spreading out of Mexico, into Central America.