People usually use qualitative terms to express spatial relations

while current geographic information systems（GIS） all use quantitative approaches to store spatial information.The abilities of current GIS to represent and query spatial information about geographic space are limited.If GIS are to be made easier to use

it must be made more intuitive

so that it will help people focus on the work they want to do without thinking about a computer program or application.In order to incorporate the concepts and methods people used to infer information about geographic space into GIS

research on the formal model of common sense geography becomes increasingly important.This paper worked on how to formalize the qualitative natural-language descriptions of spatial relations between linear geographic objects.Based on the result of a human subject test about natural-language description of spatial relations

this paper defines some quantitative topological and metric indices which are related with the natural-language spatial relation terms

and uses these indices to formalize the natural-language representation with a decision tree algorithm

thus bridging the gap between natural-language terms and the computational model of spatial relations.This method provided a way of completely understanding the relationship between the ambiguous natural-language representations and the geometric spatial relations of geographic objects.The rules extracted from the trees can be used in natural-language spatial query systems.