Abstract: lacement of annotation affects the Cartographic subsystem of GIS directly, whose most important issue for area feature is where the annotation places. This paper argues that the essence of automatic placement of annotation in area feature is one of ‘reducing dimension processing’ for 2-D symbols, i.e. the low-dimensional symbols (placement point of 0- dimension or placement line of 1-dimension) is used to describe the main characteristics of the high-dimensional symbols (area feature of 2-dimension). Via deduction based on geometrical graphics-cognitive, this paper puts forward that the placement position of annotation in area feature should make the area of internal Voronoi-cell maximum, that Voronoi diagram generated between the border of area feature and placement candidate. Because the principles can be stated by Li & Huang’s geometric information, then, on the set of quantitative measures proposed by Li&Huang, the concepts of ‘Entropy Center’, ‘ Double Entropy Centers’ and ‘Entropy Line’ have been introduced. Finally, an algorithm of automatic placement in area feature, of cause, based on (geo)metric information, has been proposed. This paper provides that algorithm has been put in to practice and gets better effect than some other optimal labeling algorithms.