In this paper I present an overview of the linguistic distance separating the Breton-speaking communities of western Brittany, France. This was achieved by applying a dialectometric approach dedicated to the quantitative analysis of dialectal data extracted from the Nouvel Atlas linguistique de la Basse-Bretagne. The literature confirms the degree to which geographical factors can have a strong influence on the distribution of dialectal features. In a previous article, I revealed that geographical parameters determine the level of linguistic similarity between small neighboring communities. In this paper, I seek to determine whether geographical factors apply also to the entire territory mapped by the NALBB. More specifically, I assess which geographical parameters contribute most to shaping linguistic similarity/distance and the extent to which these factors interact to create specific linguistic niches.