A method to compress a very large original geographic database down to a
manageable and economical size while preserving accuracy is herein
described. Similarly, a method to quickly retrieve, decompress, and
display data is herein described. An original geographic database is
prepared for compression by dividing it into discrete regions called
bounding boxes. The bounding boxes may be variable sized to improve
accuracy and compression. Absolute map coordinate data is compressed by
converting it to relative map coordinate data. Map files are named in a
descriptive manner to allow determination of map file characteristics
merely by inspecting the file name. Relative map coordinate data can be
displayed without being converted to absolute map coordinate data.
Alternately, relative map coordinate data may be quickly decompressed
into absolute coordinate data. Retrieving compressed data is facilitated
by forming view windows having adjacent load regions pre-decompressed and
ready for user display.