jats:titleAbstract</jats:title>jats:pTracing the diffusion of linguistic innovations in space from historical sources is challenging. The complexity of the datasets needed in combination with the noisy reality of historical language data mean that it has not been practical until recently. However, bigger historical corpora with richer spatial and temporal information allow us to attempt it. This paper presents an investigation into changes affecting first person non-singular pronouns in the history of Norwegian: first, individual changes affecting the dual (jats:italicvit</jats:italic>>jats:italicmit</jats:italic>) and plural (jats:italicvér</jats:italic>>jats:italicmér</jats:italic>), followed by loss of the dual-plural distinction by merger into either form or replacement of both by Danish-Swedishjats:italicvi</jats:italic>. To create dynamic spatial visualisations of these changes, the use of kernel density estimation is proposed. This term covers a range of statistical tools depending on the kernel function. The paper argues for a Gaussian kernel in time and an adaptive uniform (jats:italick</jats:italic>-nearest neighbours) kernel in space, allowing uncertainty or multiple localisation to be incorporated into calculations. The results for this dataset allow us to make a link between Modern Norwegian dialectological patterns and language use in the Middle Ages; they also exemplify different types of diffusion process in the spread of linguistic innovations.</jats:p>