GIS Data Sources: Starting Points

• ArcGIS Pro
• ArcMap Desktop
• ArcGIS Online
• QGIS
• R: Mapping and Geospatial
• Web Mapping
• Data and Visualization Services
• Introduction to Data Visualization
• U.S. Federal Government Publications
• U.S. Census
• ​Google Earth
• Google Fusion Tables
• Maps

General

• ArcGIS Hub  Thousands of free GIS datasets primarily from U.S. federal, state, and local agencies, but some international areas, too.
• GeoPlatform.gov: Colllection of over 100,000 geospatial datasets in all sort of formats, from federal and state agencies, universities, non-profits, city governments, and other entities.
• ESRI Data & Maps Layers covering the USA, international areas, and the entire world (Duke Only) 

United States

• Census Bureau TIGER Data Products Includes the TIGER/Line Shapefile boundaries for Census geographies.
• The National Map Small-Scale Data Download From the US Geological Survey (layers formerly at The National Atlas site)
• Homeland Infrastructure Foundation-Level Data (HIFLD) An open data site from the Dept. of Homeland Security with a lot of GIS layers relating to infrastructure in the United States.
• USDA Geospatial Data Gateway US Dept. of Agriculture

International

• Data by Country From DIVA-GIS
• UNEP GEO Data Portal From the UN Environment Programme

Local Area

• NC OneMap North Carolina GIS data
• Durham County, NC, GIS layers (Duke Only)
• Duke GIS layers (Duke Only)

Data for History

• Euratlas Historical Political Boundaries of Europe (Duke Only)
• NHGIS US boundary files for 1790 through 2010