  The influence of the geomagnetic field on the development of air showers is
studied. The well known International Geomagnetic Reference Field was included
in the AIRES air shower simulation program as an auxiliary tool to allow
calculating very accurate estimations of the geomagnetic field given the
geographic coordinates, altitude above sea level and date of a given event.
Some test simulations made for representative cases indicate that some
quantities like the lateral distribution of muons experiment significant
modifications when the geomagnetic field is taken into account.
