Concept or adaptive spatial unit scaling in multi-temporal thematic maps for representing change

The increasing demand for and availability of multi-temporal data is also leading to the growing importance of usable multi-temporal thematic maps. However, the respective conventional map types have a number of disadvantages, both for animated and static visualisation. The innovative approach of this research is to test an alternative graphical coding by adjusting the size of spatial (or enumeration) units according to the change of values (instead of using lightness/saturation or graduated symbols). This idea is based on the concept of Value by Area Maps, which has so far only been used almost exclusively for mono-temporal maps. The aim of this work is to develop a concept for an adaptive scaling of spatial units for the visualisation of changes. This includes the consideration of different, flexible scaling functions (proportional, exponential, range-graded) to highlight specific changes, the distinction between Total Change Maps (i.e. the total map size is changed according to the total value change) and Normalised Change Maps (i.e. the total map size is kept constant over all epochs of time) and the integration of original value data by dual coding (including an a priori data classification that preserves changes). This concept is demonstrated and discussed using a real data set. In addition, the results of a small, preliminary qualitative study are presented that confirm the general applicability of this concept and point to the necessity of further developments and future empirical studies.