Redistricting is the process of redrawing state legislative and congressional district boundaries so that the population is more or less equal in each district. This is done every 10 years by state legislatures following the U.S. Census. At the local level, each governmental body does it for its own districts.
In Alachua County, County Commission and School Board districts each have 5 residential districts and the candidates run County-wide. The City of Gainesville has 4 single-member districts, two at-large commissioners, and a Mayor elected at-large. The County Commission, the School Board, and the Gainesville City Commission are each responsible for their own redistricting.
For more information, visit the Florida House of Representatives redistricting website. Through this website you can access MyDistrictBuilder, a tool for building district boundaries.