There is disclosed a method for downloading image tile data from a server to a client device, the data being organized, by the server, in a hierarchal structure, where each level of the hierarchal structure stores a subset of image tiles associated with a particular resolution level. The method comprises, where the client device requests a new image view of a larger resolution, determining an anchor point of the first image view; based on the anchor point, determining a first anchor image tile of the first-level image tiles; using the hierarchical structure, determining a corresponding four child second-level image tiles, the corresponding four-child second-level image tiles forming a second anchor image tile; sending to the client device the second anchor image tile, the sending causing the client device to: replace, in the memory and on the output device, the first anchor image tile with the second anchor image tile.