Maryland, like all states, must draw new congressional districts (U.S. Constitution Article I, Section 2) and state legislative districts every ten years (Maryland Constitution Article III, Section 5) based on the principal of one-person one-vote following the decennial Census of the United States.
The Maryland Department of Planning (MDP) is the repository of reapportionment and redistricting maps and data products. MDP is Maryland's designated state agency coordinator for the Census Redistricting Data Program with the U.S. Bureau of the Census.
The redistricting process begins with the decennial Census count (in spring every ten years) and then the delivery of the population data in May of the following year. After holding public hearings, receiving 3rd party plans and a review and analysis of proposed plans, a Redistricting Advisory Committee is appointed by the Maryland governor and delivers proposed congressional and legislative plans to the governor. The governor then submits his plans to the Maryland General Assembly as bills for passage into law. These new districts are then adopted by the General Assembly and signed into law by the governor.
Overview of the 2010 Census Redistricting Data Program - U.S. Bureau of the Census