I'm unable to find very much data about the usage of APIs from United States federal agencies. Which APIs that have been released have the highest traffic number in terms of queries, and/or implementation?
There is a growing catalog of APIs from the federal government available at Data.gov's Developer community. Activity on each dataset will be made visible in the activity stream area (not yet visible as the new catalog was just created last week). In the meantime, you can see API activity as follows:
- EPA Envirofacts API: dataset page and activity stream
- Previous metrics (temporary solution) until the activity streams are populated
(Disclaimer: I am the Evangelist for Data.gov.)