A graphics or image rendering system, such as a map image rendering system, receives image data from an image database in the form of vector data that defines various image objects, such as roads, boundaries, etc., which are to be rendered as straight lines within an image. The imaging rendering system renders the image objects by applying an anti-aliasing technique that determines varying pixel color values at or near the edges of each straight line to be rendered on the image, so as to obtain a pleasing visual effect when rendering a road or other boundary in any orientation on the image screen. The anti-aliasing technique determines a scaling vector having values dependent on the location of a particular pixel in the image along the normal to the straight line forming a road and determines a pixel color value at each pixel location associated with the road based on this scaling vector, such that the pixel color value at each pixel in or near the line is proportional to a component of the scaling vector. This technique produces a more gradual transition in pixel color values from a non-road location to a road location in the image, and thus provides a non-aliased rendering of the road regardless of the orientation or direction in which the road is being rendered in the image.