On Feb. 19, the Pennsylvania Supreme Court adopted a new redistricting plan to be used in the state’s 2018 congressional elections. The court’s action came after it struck down the state’s existing districting plan and Tom Wolf, the state’s Democratic governor, refused to accept an alternative redistricting plan put forward by Pennsylvania Republicans, who control the state’s legislature.

In its initial order, the court warned the legislators that it would adopt its own redistricting map, created by Stanford Law professor Nathaniel Persily, were the legislature and governor unable to agree on a proposed map by Feb. 15. They did not agree. Though Republicans in Pennsylvania have filed various legal challenges to the Pennsylvania court’s decision, those challenges appear unlikely to prevail because the Pennsylvania Supreme Court based its decision on state, rather than federal, law.

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What’s the controversy? Every decade the United States conducts a census, and the results of that census determine how many representatives each state can send to the U.S. House of Representatives. After states learn that number, they determine (typically through the state legislature) how the state will be divided geographically into districts, each of which will elect its own U.S. House member. For generations, this process has been fraught with political gamesmanship as state politicians of each party try to maximize the number of districts that politicians of their party are likely to win. The U.S. Supreme Court occasionally has stepped in to provide guidelines about the legal bounds of the process, but states typically have wide discretion to draw district lines as they see fit.

This procedure has become hypercharged in recent years. With advances in computational technology, state mapmakers have become better and better able to draw sophisticated maps that maximize their party’s chance of prevailing. Using historical election returns at the precinct level, mapmakers can determine how each party would fare under every possible map and under varying assumptions about voter turnout. This process is so pervasive that the U.S. Supreme Court is currently considering the legality of maps in several states that were constructed using this method. The Pennsylvania Supreme Court’s decision relied on a similar argument, noting that statistical evidence rendered the Pennsylvania districting plan one of the most partisan in American history.

Common among all of these strategies is a general idea to make districts “safe” for the mapmaking party, ensuring that the mapmaking party has a healthy historical majority of voters in as many districts as possible, and putting many “strong” areas for the minority party into a single district. This way, the mapmaking party is likely to cede as few seats to the minority party in each election. The result are electoral districts where voters vote in uncompetitive elections because the partisan composition of the district renders one candidate far more likely to win. For example, 51 percent of Pennsylvania voters supported the Democratic candidate in the 2012 congressional election; however, the party won only five of the state’s 18 congressional seats. Because Democratic voters were so tightly packed into a few districts and “cracked” into relatively small numbers in the remaining districts, Republican voters won a disproportionate number of congressional seats.

So, what did this look like in Pennsylvania? As Andrew Prokop explains in Vox, the new map has nine districts that President Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE won by more than 5 points in the 2016 election; the old map had 11. Conversely, the new map has six districts that Hillary Clinton Hillary Diane Rodham ClintonBiden leads Trump by 36 points nationally among Latinos: poll Democratic super PAC to hit Trump in battleground states over coronavirus deaths Battle lines drawn on precedent in Supreme Court fight MORE won by 5 points or more; the old map had four. Both maps have three districts where neither candidate won in November 2016 with more than 6 points.

Or, to put it differently, there are six seats currently held by Republicans that now have a more Democratic-leaning electorate, and one district that becomes significantly safer for Republicans. On the other hand, none of the districts currently held by Democratic incumbents become in play for Republicans. Based on the new map, analyses done by FiveThirtyEight expect Democrats to win 7.5 districts over the long term, up from 6.1 under the 2011 map. Thus, it’s a map that makes Democrats more likely to win more seats in November 2018 than they would have under the existing redistricting scheme.

It’s also a map that the state will have to work quickly to implement; the filing deadline is less than a month away. However, before those elections, Pennsylvania voters in the western part of the state will go to the polls in March to select a replacement for former Republican Rep. Tim Murphy Tim MurphyBiden receives endorsements from three swing-district Democrats A federal abortion law might be needed Female Dems see double standard in Klobuchar accusations MORE, who recently resigned. Both candidates for Murphy’s 18th District, Republican Rick Saccone and Democrat Conor Lamb, live in districts represented by incumbents who will be on the ballot in the November 2018 elections. While there is no legal requirement that representatives live in the district they represent, most do — meaning that the winner of the March election will face a difficult decision about where and how to seek reelection in November.

When the legal challenges settle, the candidates have filed, and the campaigns have been waged, one thing seems clear: more Pennsylvania voters will have the opportunity to vote in a competitive U.S. House election in 2018 under the new map than would have done so under the existing map, suggesting that interest and attention to these elections will be high, both in the state but also nationally as Democrats look to flip every seat they can as they seek to regain control of the U.S. House.

Michael J. Nelson is the Jeffrey L. Hyde and Sharon D. Hyde and Political Science Board of Visitors Early Career Professor, an assistant professor in the Department of Political Science, and a member of the affiliate law faculty at The Pennsylvania State University.