A method for displaying a map on a mobile client device includes storing map
data
on a server, the map data defining objects appearing in the map and comprising
vector coordinates of the objects in a predetermined frame of reference. Upon receiving
at the server a request from the client device to provide a map of an area along
a route on which a user of the client device is to travel, a heading of travel
of the user on the route is determined, and the vector coordinates are transformed
on the server into a rotated frame of reference, which is approximately aligned
with the heading of the user. A portion of the map data corresponding to the area
along the route and including the transformed vector coordinates is downloaded
to the client device from the server. An image of the area of the map in the rotated
frame of reference is rendered on the client device, based on the downloaded map data.
