Chapter 6: Tile-Based Mapping with Opacity
Andrew Clouston¹, Michael P. Peterson²
¹Geography, Environment and Earth Sciences, University of Victoria, Wellington, New Zealand
²Department of Geography/Geology, University of Nebraska at Omaha, Omaha, USA
Splitting maps into small contiguous tiles increases the speed of Internet map distribution, improves the panning of the map, and facilitates the presentation at multiple scales. This online method of map distribution was introduced by Google in 2005 and all the major online-mapping services including Bing, Yahoo, OpenStreetMap, Nokia, and MapQuest have since adopted the technique. User-generated tiles can be overlayed on top of these maps, obscuring the standard map or satellite views. Any digital map whether a scanned historic one or a computer-generated thematic map can be converted to tiles. A multilevel overlay can be created by tiling several different maps or orthophotos. By enabling the presentation of more targeted map information, such overlays are an increasingly important method of map presentation through the Internet.
A significant disadvantage of tiled overlays is that they totally obscure the underlying base map. By providing an interactive tool to control level of opacity on tiles, the cartographer can effectively combine two views. Benefits include, image comparison, map merging, and masking effects. The combination of tile mapping and opacity control provides a new way of enabling user interaction with online maps and provides a valuable new tool for the modern cartographer.
Keywords: Interactivity; Opacity; Overlay; Tilemapping.