The Tile-Based Mapping Transition in Cartography - Maps for the Future Children Education and Internet - page 154

Fig. 13.2 A 2001 version of the MapQuest webpage. Dominated by ads, the map constitutes only
a small part of the webpage. Three different maps of southern Florida are also depicted. A total of
ten zoom levels were available

the image is actually composed of square pieces. With a slower Internet connection,
the individual tiles are clearly evident.
The basic street map is the most functional of all the views provided by these
services. The map is provided in up to 20 scales called levels of detail (LOD). Each
map at a particular level of detail is rendered from an underlying vector database
consisting of points, lines and areas. This map is converted into a grid representa-
tion by placing the points, lines, and areas into a matrix of pixels. In the process,
anti-aliasing is performed by adding lighter pixels around sharp edges to soften the
stair-step effect. After the map is placed in a matrix that can be millions of pixels on
each side, it is divided into tiles—usually 256 256 pixels (see Fig. 13.3 ). This

process is repeated for every LOD.