The Tile-Based Mapping Transition in Cartography - Maps for the Future Children Education and Internet - page 155

Large Raster

Individual
tile

Vectors

256

256

points lines areas

Rasterization

Fig. 13.3 The process of making map tiles. A database of points, lines and areas is rasterized into
a large matrix that is subsequently divided into 256 256 square tiles

Fig. 13.4 Individual map tiles from Google Map at six different levels of detail (zoom levels). In
2005, Google introduced a tiling system to deliver online maps. Over a trillion tiles are used for
Google's 20 zoom levels

Figure 13.4 depicts a series of Google Map tiles at different scales. All tiles are
256 256 pixels and require an average of 15 KB a piece to store in the PNG format.

Table 13.1 shows the number of tiles that are used in a tile-based mapping system
for 20 levels of detail (LOD), or zoom levels, and the associated storage
requirements and storage costs. With 20 LODs, there are a total of approximately
1 trillion tiles for the whole world. At an average of 15 KB per tile, the total memory
requirements would be 20 Petabytes, or 20,480 Terabytes. No single client