How often are congressional districts determined? What are they based upon? Is it done in a fair and equitable manner? When it's done in a...

Congressional districts are determined every ten years.  This happens as the result of the United States census.  The census is conducted every 10 years (the last one was 2010).  When the census is conducted, the congressional districts are redistributed among the 50 states.  If a state gains or loses a seat or seats, the districts have to be redrawn. 

Ideally the redistricting is done strictly on the basis of geography and population.  The people who redistrict would just create districts with equal populations and relatively compact boundaries.  Instead, however, there is typically a great deal of gerrymandering, in which political parties try to draw the districts in a way that will help them politically.  The term “gerrymandering” comes from Elbridge Gerry, a signer of the Declaration of Independence.  He was a politician in the early United States who was allegedly responsible for creating an oddly-shaped electoral district in Massachusetts.