Element sets 
from map space 
Element sets 
from geographical space 
Element sets 
from attribute space 
Element sets 
from graphic space 
Fig.1: A basic relational model describing the raster-based choropleth mapping process in the form of a structure 
graph. The nodes constitute sets of elements, the edges between them indicate relationships. They are characte 
rized by the type of correspondence: 1 1 means one—one, m 1 many—one(i.e. , 1,2,3,-•• to l), me 1 con 
ditional many-one (0,1,2,... to l), c 1 conditional one-one (0,1 to 1) (symbolism after THURNHERR and ZEH- 
DER 1979). A full extensive description of the relations is provided in tabular form as indicated by Ti (i = 
1,...,8).