Open data

Open data is data, most often from a government agency, that is published in a machine-readable format under a license or policy allowing anyone to access, use, and redistribute it, typically at no cost. Common examples are city budgets, transit schedules, crime incident logs, permit records, and 311 service requests.

It is usually published as CSV, JSON, or GeoJSON files on a data portal, organized in a data catalog, and increasingly made available through an API integration so applications can pull current data rather than downloading static files. Open data overlaps with, but is not the same as, administrative data: administrative data is collected as a byproduct of running a program, and only some of it is ever released publicly as open data, since privacy, security, or legal restrictions keep most administrative records closed. Different open-data bodies and standards define the underlying principles somewhat differently, but they generally agree on accessibility, machine readability, and freedom from restrictive licensing.

Open data underpins civic-tech applications, journalism, academic research, and government transparency and accountability efforts, and detailed datasets like the American Community Survey or local census tract statistics are frequently distributed this way. The main pitfalls are that "open" does not guarantee quality: portals can host stale, undocumented, or inconsistently formatted datasets, and releasing granular data can create re-identification risk for individuals even when direct identifiers have been removed.