The Sixth International Symposium on Spatial Databases (SSD'99) was held in Hong Kong, China, July 20-23, 1999. This is a \ten-year anniversary" edition. The series of conferences started in Santa Barbara in 1989 and continued - annually in Zu ]rich(1991), Singapore (1993), Portland, Maine (1995), and Berlin (1997). We are very pleased that on this occasion Oliver Gun ] ther, one of the initiators of the conference in 1989, agreed to give an \anniversary...