Tiling System
From World Wind Wiki
World Wind's tiling system can be summarized with the following picture. Note that this picture comes from the original World Wind documentation, not the Java version, but since this hasn't changed (apart from the naming convention, see below), it doesn't really matter.
Note that "Layer Number" in the picture should be "Level Number". Same with "Each additional layer quadriples..." - should be "Each additional level quadriples..."
[edit] Tile naming convention
Note that the example tile name given in the above picture is using the .net naming convention. For the Java version, the leading zeros have been dropped, so the equivalent tile name for WWJ is BlueMarbleTextures\0\2\2_7.dds. See here for a program that can convert WW cache packs to the WWJ's naming convention.