Finding sources of open data can be a little cumbersome because there are so many ways to find data. There are a lot of websites that house data. For instance, let’s say that you are looking for data on the bike routes in Philadelphia. One place you can look at is Open Data Philly which is a portal that provides access Philadelphia based data sets, APIs, and applications. You can search amongst the over 170 datasets or even submit or nominate a dataset to be included on the site. A quick search on the site shows that there are 6 datasets related to biking ranging from bike rack locations to commuting routes. Many large cities and counties are have websites where they store open data for their municipalities.
Here are some sites for local/federal government data:
Philadelphia: Open Data Philly
New York City: NYC Open Data
Boston: City of Boston
District of Columbia: Open Data Catalog
U.S. Government: Data.gov