10 Things You Need to Know Before Drawing Next Year's Maps.

• Author: Underhill, Wendy
• Position: REDISTRICTING

A year from now redistricting will be full steam ahead, with the focus on where the boundaries for legislative and congressional districts will be set for the next 10 years. When the 2020 census data is released to the states, no later than March 31, 2021, it's go-time for redistricters.

This year, state legislatures are revving their engines, preparing and practicing for the real deal coming next year. Lawmakers are considering their software choices, gathering data, training personnel and figuring out how the public can have its voice heard during this most political of government actions.

Here's what legislators need to keep in mind for the big job ahead.

1 | States Are in Charge

The states--not Congress--unequivocally drive the redistricting bus. It's in Article 1, Section 4 of the Constitution: "The Times, Places and Manner of holding Elections for Senators and Representatives, shall be prescribed in each State by the Legislature thereof." The Constitution doesn't say how redistricting is to be done, but it's clear on who is to do it.

Although legislative redistricting is outside their purview, members of Congress have introduced bills to influence congressional map-drawing. Last year, for example, HR 1, the For the People Act, called for commissions to do congressional redistricting. The bill made its way through the House quickly but is unlikely to be taken up by the Senate this year.

2 | Lawmakers Take the Lead

Legislatures are the traditional entities to do redistricting--and they'll continue to do so in the next cycle. Lawmakers will vote on congressional maps in 41 states and on legislative maps in 36. The other states have commissions with primary responsibility for line-drawing. But even in many of those, the legislature has a role in selecting commissioners.

3 | The Census Data Matters

Article 1, Section 3 of the Constitution calls for an "actual Enumeration" of the people living in the U.S. every 10 years. The data generated by that enumeration, or census, is used in many ways, including to distribute more than $1 trillion in federal funds to the states annually through a variety of programs.

From a redistricting standpoint, the census block--the smallest geographic level--is the equivalent of a single-hump Lego. The tussling associated with redistricting is over how to build those census blocks into districts. For the coming census, bipartisan support from the states for the Census Bureau's work has burgeoned. Forty-seven...