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A Brief History of GIS

• http://www.esri.com/news/arcnews/fall12articles/origins-of-the-canada-geographic-information-system.html

Definition of Layer

• http://support.esri.com/en/knowledgebase/GISDictionary/term/layer
• http://www.esri.com/news/arcnews/fall04articles/arcgis-raster-data-model.html

ArcGIS Online

• http://www.whitehouse.gov/the-press-office/2014/05/27/white-house-science-fair-fact-sheet-backgrounder