https://www.data.gov/

How are the datasets in Data.gov collected?Under the terms of President Obama’s Executive Order and the Administration’s Open Data Policy, all newly-generated government data are required to be made available in open, machine-readable formats, while continuing to ensure privacy and security.

Federal agencies are also required to:

• Create a Single Agency Data Inventory. Agencies are required to catalogue their data assets, just like they would inventory computers or desk chairs, to better manage and use these resources.
• Publish a Public Data Listing. On their agency.gov/data pages, agencies are required to publish a list of their data assets that are public, or could be made public.
• Develop New Public Feedback Mechanisms. Agencies are required to set up feedback mechanisms to engage the public about where agencies should focus open data efforts, such as facilitating and prioritizing the release of datasets. Agencies are also required to identify public points of contacts for agency datasets.

Agency Public Data Listings, on agency.gov/data pages, are harvested into the central catalog for Data.gov.  Each agency is responsible for its own data.