Patent ID: 7199800

Claim:
A map display unit including a first memory for storing map data and a drawing memory for drawing the map data and displaying display-area data of a drawing area in the drawing memory on a display, comprising: data-reading means for selectively reading compressed map data and uncompressed map data from a data storage medium; data-decompressing means for decompressing the compressed map data read out by the data-reading means and storing the decompressed map data in the first memory; drawing means for drawing either of the uncompressed map data read out by the data-reading means or the map data stored in the first memory in the drawing memory; display-control means for determining the display area and displaying the display-area data of the drawing area in the drawing memory on the display; and map-selecting means for selecting a map to be displayed, wherein the map-selecting means switches which of the uncompressed map data or the map data the drawing means draws in the drawing memory; wherein the map-selecting means includes means for determining the velocity of a vehicle and switches the map to be displayed depending on whether the velocity has exceeded a threshold.