For the heigtmap I combined two images from the NASA Blue Marble collection, the topography and the bathymetry.
You can find the images here (external link). I changed the images a little bit to fit better. For example, on the 1:1000 scale, the lowest point is 9, the highest point is 254. On the 1:4000 scale, the lowest point is 48, the highest point is 110. This way, the mountains looks better on each scale.