Self-organizing maps (SOM) or Kohonen maps are a type of artificial neural network (ANN) that mixes in an interesting way the concepts of competitive and cooperative neural networks. A SOM behaves as a typical competitive ANN, where the neurons fight for a case. The interesting twist added by Kohonen is that when a neurons wins a case, the prize is shared with its neighbors. Typically, the neighborhood is bigger at the beginning of the training, and it shrinks in order to let the system converge to a solution. One of the most interesting applications of this technique is applying it to the Travelling Salesman Problem, in which we can use a coordinate map and trace a route using the neurons in the ANN. By defining weight vectors as positions in the map, we can iterate the cities and treat each one as a case that can be won by a single neuron. The neuron that wins the case gets it weight vector updated to be closer to the city, but also its neighbors get updated. The neurons are placed in a 2D space, but they are only aware of a single dimension in their internal ANN, so their behavior is like an elastic ring that will eventually fit all the cities in the shortest distance possible.