Maps representing geography based analysis are mostly composed of multiple layers overlaid together to represent the information.  Most of these maps have atleast two distinct set(s) of layer, which can be termed as Base layers and Information layers. Base layers represent geogrpahical or administrative boundaries, even rivers or roads etc. and are offered by map providers like Google Maps, Bing Maps, Yahoo! Maps and Open Street Maps.  Below image aids to understand this concept (thanks to iconarchive.com for the icon).

While base layers represent publicly known information like city, state or country boundaries, information layers are more related to proprietary information catering to specific contextual use-cases for specific audience or organization.
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