(also bit map)
When I first heard this term, it would strictly refer to saving storage space or sometimes to search techniques. Nowadays, it is much more likely that the usage is related to graphics creation or display.
To my mind though, a bit map is truly a one to one mapping of conditions to individual bits. For example, to store information about whether 8 items are "in stock", a one byte field, with each bit mapped for a specific item, is sufficient. When you need multiple bits (let's say 3 bits per item), I'd call that a bit field, not a bit map. However, my opinions on that are no longer the majority way of thinking, which is why bit maps and graphics (which will require multiple bits to determine color of just one pixel) are now so related.
An interesting bit mapped search technique involves hashing text and setting bits for words that COULD be in a certain paragraph or section. If the bit corresponding to the desired word is 0, then there is no need to examine the actual text. If it is set, the word could be present, and the text is then read to do the final check.
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More Articles by Tony Lawrence © 2011-07-07 Tony Lawrence