 All records in a bucket can be indexed by either their city (which is the same for all records in the bucket), and the streets in that city whose names begin with the same letter.A grid file can be used to provide an efficient index for this structure, where records come in groupings of 26, each of them relating to street names in a city starting with one of the letters of the alphabet.This structure can be thought of as an array, table, or grid with two dimensions which we will call the x and y axes.