Finding authoritative datasets

Sharing GIS data was a difficult proposition in the past, as if you didn't have your own infrastructure, there wasn't a central place where people could share GIS data. This meant that most data lived as a hyperlink to a .zip file of a shapefile or a .kmz file, being hidden deep within a website not devoted to GIS. The age of the file was sometimes unknown, because there was no metadata or nothing on the website that told you whether the files were being updated or when they were created. With the introduction of ArcGIS Online, people and organizations have a central place where they can share GIS data and give the burden of hosting and serving the data to Esri. There are also many websites that use open-source solutions to serve out data in the form of a web mapping service (WMS) or a web feature service (WFS).