The reference point maps show the linguistic distances from one chosen site to all other sites in the data set. In the drop down list after 'Place:' a site can be chosen. The map displays the chosen reference site with a star. All other sites are colored with a scheme were the sites with the smallest linguistic distance to the reference site are the darkest and the sites with the largest distance to the reference site are the lightest (see whole color range). By checking 'Reverse colours' you get the opposite color scheme.
In addition to the map a scatter plot is created displaying the relationship between geographic and linguistic distances between the reference site and all other sites. Blue line? Local regression?
Reference(s): Goebl 1993, Goebl 2006
As default method the linear distances are displayed. 'quadratic' 'zero-based linear' 'zero-based quadratic'. [What are the other methods and why are they useful?]