Abstract: Spatial query optimization is one of the key topic in spatial database. Query optimization technology based on query cost estimation is an important method to improve the efficiency of ctueries. But the key problem of ctuery cost estimation is to estimate the size of ctuery results(i. e. selectivity). This paper focused on the two queries operations; spatial selection and spatial join,which arc most commonly used in spatial database. The paper expatiated some histogram algorithms for selectivity estimation of spatial ctueries, and analyzed their advantages and disadvantages. In the end of this paper, we discussed the future research directions of the selectivity estimation for spatial queries.

Key words: Spatial query, Histogram, Selectivity estimation, Spatial query optimization