A method for the localization of a portable device transported by an individual, which comprises: - detecting a displacement associated with a movement of said individual; - recording environmental signals during said movement, said environmental signals forming a detected time series; - applying said displacement to the particles of a particle filter only at the end of said movement; - assigning a similarity index to each particle of said particle filter, said similarity index of each particle being a parameter having a value proportional to the similarity of said detected time series with a mapped time series which consists in a time series derived from a pre-constructed map and corresponding to the time series that would be detected by said individual moving along the trajectory of said particle during said movement; - performing an operation of resampling of the particle filter which comprises making a selection of particles having a value of the similarity index that is greater than a first predefined value; - assuming the position of said individual to be the centre of a group of particles, of said selection, grouped according to a predetermined criterion; characterized in that the mapped time series are selected by: - first extracting from the map the time series corresponding to each particle of the particle filter assuming the particle to be in movement along a rectilinear trajectory which starts from the last of its assigned coordinates and arrives at the coordinates resulting from the application of said displacement complemented by the movement direction; - then aligning, for each extracted time series, said time series extracted from map with said detected time series and calculating for each of the extracted time series the similarity index of the particle to which the extracted time series is associated; wherein said predetermined criterion provides for the formation of groups of particles having a reciprocal distance that is less than a second predefined value; wherein said formation of groups of particles provides for a grouping step which comprises: - during an initialization step, associating each particle with a group to which only said particle itself belongs; - reiteratively associating with a same group all the particles having a reciprocal distance less than said second predefined value; - interrupting the reiteration when there is no group consisting of a single particle which has a distance to the other particles smaller than said second predefined value; - assuming the position of the portable device to be the geometric centre of the most numerous group of particles. - detecting a displacement associated with a movement of said individual; - recording environmental signals during said movement, said environmental signals forming a detected time series; - applying said displacement to the particles of a particle filter only at the end of said movement; - assigning a similarity index to each particle of said particle filter, said similarity index of each particle being a parameter having a value proportional to the similarity of said detected time series with a mapped time series which consists in a time series derived from a pre-constructed map and corresponding to the time series that would be detected by said individual moving along the trajectory of said particle during said movement; - performing an operation of resampling of the particle filter which comprises making a selection of particles having a value of the similarity index that is greater than a first predefined value; - assuming the position of said individual to be the centre of a group of particles, of said selection, grouped according to a predetermined criterion; characterized in that the mapped time series are selected by: - first extracting from the map the time series corresponding to each particle of the particle filter assuming the particle to be in movement along a rectilinear trajectory which starts from the last of its assigned coordinates and arrives at the coordinates resulting from the application of said displacement complemented by the movement direction; - then aligning, for each extracted time series, said time series extracted from map with said detected time series and calculating for each of the extracted time series the similarity index of the particle to which the extracted time series is associated; - first extracting from the map the time series corresponding to each particle of the particle filter assuming the particle to be in movement along a rectilinear trajectory which starts from the last of its assigned coordinates and arrives at the coordinates resulting from the application of said displacement complemented by the movement direction; - then aligning, for each extracted time series, said time series extracted from map with said detected time series and calculating for each of the extracted time series the similarity index of the particle to which the extracted time series is associated; - during an initialization step, associating each particle with a group to which only said particle itself belongs; - reiteratively associating with a same group all the particles having a reciprocal distance less than said second predefined value; - interrupting the reiteration when there is no group consisting of a single particle which has a distance to the other particles smaller than said second predefined value; - assuming the position of the portable device to be the geometric centre of the most numerous group of particles.