[Editor's note: I'm working on a group base map project that will be released in October that is for mapping at the 1:10,000,000 (1:10m) scale and smaller (regional continental to global at small print dimensions). I want this data to be easily used with online mapping services, but converting Google map tile set "levels" to natural scale equivelants isn't obvious. I remembered seeing this table at last year's NACIS conference in Missoula, Montana. Charlie Frye was kind enough to remind me where to find it on the ESRI site.]
Republished from ESRI Mapping Center.
As you zoom in (or out) of the online maps you see on Virtual Earth (VE) or Google Maps (GM), you are actually seeing a series of different maps with slightly different information displayed at each zoom level. Zoom level is indicated and controlled in an online map by the vertical zoom slider, like the one shown at the left in the image here. Whenever the zoom level is changed, a different map is shown.
Of course, these maps are well designed so that viewers are largely unaware that they are seeing these different maps. The foundation for good design of an “online map” hinges on understanding how to design for each of the zoom level represented in the entire online map. Colors, fonts, number of and types of features, etc. are all seriously considered when each of the maps is created for each of the zoom levels.
When authoring this kind of online map with ArcGIS, a map document containing group layers, one for each zoom level, is a good approach. (The Working with layers and scale ranges blog entry provides a good overview of how to organize a map document this way.) Each zoom level in the online map is represented by your work at a specific map scale in the ArcMap document. The hard part is to figure out which zoom level matches to which map scale. There are twenty zoom levels for Virtual Earth or Google Maps. The corresponding map scales that you would design and create your maps at if you wanted them to mash up on VE or GM are: