Abstract: In this paper,the method of optimum placement for pattern cell of linear symbols and the technique of the common spatial relations between two linear symbols are given,based on the character of decomposition and combination of linear symbols and the experimentation of program with Visual C⁺⁺ 6.0.According to Gestalt theory,the arithmetic of optimum placement for virtual linear symbols is discussed.The decomposition and combination of linear symbols is discussed.Two characters are described and several items of rules of optimum placement for virtual linear symbols are given.It is a common method of placement for almost all the lineal symbols which are located with their essential cell circularly collocating along the line.But these will bring about some questions when making use of the method,such as overlap,blank phenomena near those points whose trend change is evident,etc.So it is necessary to find a new arithmetic to overcome these shortcomings and make linear cartographic symbol more pleasing in vision.In this test,we have brought forward a new method of optimum placement for linear symbols and carried out it by Visual C++6.0.In order to explain the new method,this paper gives an example by writing out the algorithm of optimum placement for the dashed linear symbols.According to Gestalt theory,these points whose change trend is distinct must be placed by solid line in the dashed linear symbol.It is stipulated that the half of length of solid line is arranged in each side of those characteristic points at first.Of course,during the program for optimum placement,the length of the symbolic cell has to be adjusted in the range of visual error.Moreover the paper brings forward some methods to dispose the spatial relations between linear symbols.There are two spatial relations:intersection relation and shared-line relation.Finally,the characters of compounding of the linear object and the trait of compilation of the linear cartographic symbols are discussed.