Geography is at the heart of all Census Bureau data. All of our data sets pertain to very specific geographies that embody very specific geographic concepts.  Although we try to make using our API as intuitive as possible, the greater your understanding of these concepts, the more powerful you become as a developer using these data.

Every query must include a geography, and this API supports both FIPS and GNIS geography codes.

To query the API your request URL query string must include a for argument which defines the geography level and FIPS code(s).

For example:

/api.census.gov/data/2010/sf1?&key=...&get=P001001&for=state:06

will find the total population for the state of California.

The "for" argument may include additional FIPS codes, separated by a comma.

For example:

//api.census.gov/data/2010/sf1?&key=...&get=P001001&for=state:06,24

will find the total population for the states of California and Maryland.

In some cases you must also include an in argument to fully qualify the geography.

For example:

//api.census.gov/data/2010/sf1?&key=...&get=P001001,NAME&for=county:001& in=state:06

You will find the total population for Alameda County in the state of California.