Different entities are in charge of drawing the district lines in different states. And those differences in who draws the lines can lead to some sizable differences in where the lines are drawn.
In most states, the state legislature has primary control of the redistricting process, both for state legislative districts and for congressional districts. 34 state legislatures have primary control of their own district lines, and 39 legislatures have primary control over the congressional lines in their state (including seven of the states likely to have just one congressional district).
In most of these states, district lines pass just like regular legislation, with a majority vote in each legislative chamber; the first draft is often done by legislative committees chosen by (and under the exceedingly watchful eye of) legislative leadership. And usually, these bills are subject to a veto by the Governor (and, potentially, override by the legislators: override thresholds range from a simple majority to 2/3).
Connecticut and Maine both require supermajorities, of two-thirds in each house, to approve a redistricting plan; in New York and Washington, the legislature can override other bodies with a supermajority, and in Ohio, a bipartisan supermajority takes a first shot before another commission takes over. And five of the states above — Connecticut, Florida, Maryland, Mississippi, and North Carolina — set district lines by joint resolution, without the potential for a gubernatorial veto.
Four of the states above — Iowa, Maine, Utah, and Vermont — appoint advisory commissions, to help advise the legislature about where the district lines should be drawn. (In most states, legislative committees draft initial redistricting plans, just like they draft most legislation. But in these states with advisory committees, non-legislators are also invited to formally participate on the initial drafting body.)
Advisory commissions recommend district plans to the legislature, but the legislature has the final say. The commissions vary widely: some are created by statute (and can be changed or eliminated by the legislature), and some are written into the state constitution. And some (like Iowa) amount to a much stronger (and more independent) default than others.
If advisory commissions influence redistricting maps before they go to the legislature, backup commissions have their influence afterward. In eight of the states above — Connecticut, Illinois, Maryland, Mississippi, Ohio, Oklahoma, Oregon, and Texas — there are special backup procedures to draw state district lines if the legislature does not successfully pass a plan. (Connecticut, Indiana, and Ohio use backup commissions for congressional districts.) Usually, a specific deadline in the state constitution triggers the backup commission’s work.
These backup commissions all look a bit different. In Maryland, redistricting falls to the Governor’s preferred plan if the legislature fails to act. In Oregon, the Secretary of State is the backup actor. In Connecticut and Illinois, the backup commission is composed of members selected by the legislative leadership. In Mississippi and Texas, the backup commission includes specific statewide elected officials, like the State Treasurer or state Attorney General. In Ohio and Oklahoma, these models are blended, with a backup commission composed of specific statewide officials and several members selected by the legislative leadership.
In all of the states above, the legislature is primarily in charge of redistricting. Elsewhere, some other entity draws the lines. Seven states — Arkansas, Hawaii, Missouri, New Jersey, Ohio, Pennsylvania, and Virginia — draw state legislative districts with so-called “politician commissions,” where elected officials may serve as members. (Hawaii, New Jersey, and Virginia use politician commissions for congressional districts.)
Each, again, is a bit different. In Arkansas and Ohio, specific elected officials have designated seats on the commission. In the other states, the legislative or party leadership nominates at least some commissioners, usually with balanced numbers from each party, and sometimes with a role for the Governor or Chief Justice of the state Supreme Court to select nominees or appoint additional members of the commission.
In Virginia, the commission consists of eight legislators and eight more independent citizen commissioners — because any plan must be approved by six of the eight legislative commissioners and six of the eight citizen commissioners, it may end up in practice functioning more like an independent commission.
The remaining states — Alaska, Arizona, California, Colorado, Idaho, Michigan, Montana, New York, and Washington — all draw both state and federal districts using an independent commission, with regulations limiting direct participation by elected officials. (Alaska and Montana currently have only one congressional representative, and do not need to draw congressional lines; if Alaska did gain more than one seat, the legislature would draw its congressional lines.)
Members of these commissions are neither legislators nor public officials. Each state other than Colorado and New York also bans commissioners from running for office in the districts they draw, at least for a few years after the commission finishes its work.
Some of the states further limit commission members’ link to the legislature: Arizona, California, Colorado, Michigan, and New York, for example, also bar legislative staff from serving on the commission; California, Colorado, Idaho, Michigan, New York, and Washington bar lobbyists from serving on the commission as well.