

Object( x, y, otherattributes ) // x and y are the // coordinates of the object 


(The point with the smallest xcoordinate value is the leftmost leaf key)
(The point with the smallest ycoordinate value is the leftmost leaf key)




Total area of the grid = 1000 × 1000 = 1,000,000 Selected area = 100 × 100 = 10,000 = 0.01 × Total area 


Comment:


How to find all point in the selected region:
while ( not EOF ) { Read next data block; // Scan ALL data blocks !! for ( each point (x,y) ∈ data block ) { if ( 450 ≤ x ≤ 550 && 450 ≤ y ≤ 550 ) Output (x,y); } } 
There are 1,000,000 points 1 disk block stores 100 points # disk blocks used = 1,000,000 / 100 = 10,000 blocks 
So we would need access:
10,000 disk blocks.... (Compare this number to 11,000 blocks when using B^{+}trees !!) 
So using the Btree index does not help us improve performance !!!
