This year, on the first day of its term, the Supreme Court will consider the much-anticipated Gill v. Whitford. That case brings up the hot-button question of whether a state legislature may draw electoral districts that favor one party over another. Gerrymandering, as it’s called, is clearly prohibited if it’s done to dilute the votes of racial groups. But when it comes to partisan gerrymandering, the Supreme Court, while willing to hear some challenges, has so far been unwilling to declare such a plan to be an unconstitutional partisan gerrymander. A decision on Gill affirming the lower court — or setting a new standard and remanding the case for further review by the lower court — has the potential to change that.

Before the Supreme Court weighs in, let’s look at how other countries redistrict. How does redistricting differ in the United States from elsewhere? Are there lessons for Americans in these varying experiences and procedures?

According to the Supreme Court, the Constitution requires that population must be equalized across districts. The idea is that if one Arizonan lives in a district with 1 million other voters while another Arizonan lives in a district with only 200,000 other voters, the second one’s vote is more influential in choosing a member of Congress. Of course, populations shift, growing or shrinking over time.

To prevent those shifts from leaving unbalanced districts, state legislatures must redraw their electoral districts every 10 years, after the Census Bureau releases its new population data. Redistricting regularly leads to heated political and legal fights as legislators scramble to gain advantage for their parties.