The present paper focuses on conservative and innovative (transitional) dialect areas and the questions of 1) how such areas can be methodologically visualized and 2) how the outcomes can be interpreted. In the first part of this paper a geostatistical method of representing phonological features in space will be introduced: interpolation. This method is not entirely new to dialectology; it has been quite neglected, though, in comparison to other methods of mapping, such as the isogloss or dot symbol method that was mainly used in traditional dialect atlases. The interpolation method will be applied to a large corpus of spontaneous speech data from rural dialects spoken in southwest Germany. Methodological steps in data processing will be described, resulting in a data set that can be used as input for statistical analysis and the visual depiction of variation in space as interpolated grid plots. In the second part results will be discussed. The major outcome consists of an aggregate interpolation plot that includes variables from fifteen different etymological sound classes. These sound classes can be used for demonstrating the distribution of receding phonological variables in space. The interpolation shows two conservative areas where receding forms are still widespread. They lie within the centers of the two major dialect groups of southwest Germany: Alemannic and Swabian. The conservative areas are separated by a broad transitional zone characterized by intense variation between receding and innovative variants. It will be argued that this transitional zone is not due to the horizontal spread of the dialects into each other’s areas alone. Rather, variation is triggered by vertical standard influence that supports any dialect form to spread out horizontally as long as it is phonologically identical or similar to the standard form.