Willem Grootaers was trained in dialect geography by his father Ludovic who founded the Southern Dutch center in 1922. Ludovic Jean Joseph Grootaers was the first who collect southern Dutch dialect material in a systematic way (Goossens & Van Keymeulen 2008). In 1950 Willem came to Japan, and in 1965 he became a researcher at the National Institute for Japanese Language Research. As an interviewer he contributed to the Linguistic Atlas of Itoigawa (Sibata 1988-1995).
Dialectometric studies rely heavily on systemetically collected material. In the period 2008–2011 we compiled a large database of dialect recordings for 86 local dialects of Dutch spoken in the Netherlands and the northern part of Belgium (‘Flanders’). In each of the 86 locations two older male speakers and two younger female speakers were recorded, representing conservative dialect speakers and innovative dialect speakers respectively. Using these data we analyze and visualize the change of dialect areas in apparent time by using a new flavour of bootstrap clustering. In our approach 1) we consider dialect groups as continua, i.e. each local dialect is not necessarily strongly related to any other local dialect in the same group; the local dialects in a group rather constitute a 'network' and 2) we take into account that not every local dialect can be classified with statistical confidence.