Similarity of spatial relations is with wide applications in normal life.Research on similarity assessment of exact direction relations is more perfect

but the presented methods based on crisp regions can not deal with the approximate direction relations.Based on the extended direction relation matrix(EDRM)

the paper proposed a method for similarity assessment of approximate direction relations

and then the algorithm SA-EDRM was implemented;on the basis of the variation of location and scale of the target object

different scenarios were generated to test SA-EDRM

and the experimental results verify the effectiveness of the algorithm.In the end

an instance of Agricultural GIS was used to explain the practical value of this article.