The Tile-Based Mapping Transition in Cartography - Maps for the Future Children Education and Internet - page 161

Fig. 13.7 Comparison of two different overlays. The top map showing traffic is transparent
allowing the underlying street map to be visible. The bottom map showing bicycle paths is opaque,
at least in urban areas. Both overlays are supplied in multiple levels of detail
13.4 Summary
The advantage of using a major online mapping site is that the maps represent a
common and recognizable representation of the world. Overlaying features on top
of these maps provides a frame of reference for the map user. A particular
advantage for thematic mapping is the ability to spatially reference thematic data.
For simplicity, thematic maps have limited the display of spatial reference data such
as the location of cities and transportation networks. This has made it more difficult
for map users to spatially reference thematic data.
Storing the online map represents a major expense for online map providers.
Depending upon the method of storage, the cost for simply storing the map may be
as much US $630 million. Maintenance of the database and a variety of other costs
would represent significant on-going costs. A non-profit agency or government