A single-member district (SMD) system is an electoral arrangement where each geographic district elects exactly one representative, which tends to advantage large parties and push the system toward two-party competition, as seen in the UK and Nigeria in AP Comparative Government.
In a single-member district system, the country gets carved into geographic districts, and each district sends exactly one person to the legislature. One district, one seat, one winner. Everyone else in that district who voted for a losing candidate gets no representation from that race.
That winner-take-all logic is why SMD systems squeeze out smaller parties. A third party could win 15% of the vote nationwide and still get almost zero seats, because 15% rarely wins any single district outright. Over time, voters learn not to 'waste' votes on parties that can't win districts, and the system settles into two dominant parties. In the AP Comp Gov course countries, the UK elects its House of Commons through single-member districts (using first-past-the-post rules), Nigeria uses single-member districts for its legislature, and Iran's Majles mixes single-member and multimember districts, sometimes requiring a second round of voting (DEM-2.A.1).
This term lives in Topic 4.1 (Electoral Systems and Rules) in Unit 4: Party and Electoral Systems and Citizen Organizations, supporting learning objective AP Comp Gov 4.1.A, which asks you to describe electoral systems and election rules among course countries. SMD is one of the biggest comparison tools in the whole course. Once you know a country uses single-member districts, you can predict things about its party system (fewer, bigger parties), its legislature (often a clear majority for one party), and its third parties (structurally disadvantaged). The exam loves cause-and-effect reasoning like that. Electoral rules aren't trivia; they're the machinery that shapes who holds power, which is the core question of comparative politics.
Keep studying AP® Comparative Government Unit 4
First-Past-the-Post (Unit 4)
FPTP is the rule that usually runs inside single-member districts. SMD answers 'how many seats per district?' (one) and FPTP answers 'how do you win it?' (most votes, no majority needed). The UK's House of Commons elections combine both.
Majles Elections in Iran (Unit 4)
Iran proves SMD doesn't have to mean FPTP. Majles members are elected in single-member and multimember districts, and races sometimes go to a second round of voting. So one seat per district, but a runoff instead of a simple plurality win.
Guardian Council (Unit 4)
In Iran, the district map matters less than who's allowed on the ballot. The Guardian Council vets all Majles candidates before voters ever see them, which is a reminder that electoral rules in some regimes are structured to advance political interests, not just count votes.
Gender Quotas and Proportional Representation (Unit 4)
SMD is the foil for proportional representation. PR systems hand out seats to match vote shares, which lets small parties in and makes party-list gender quotas easier to enforce. SMD systems make both of those much harder.
Single-member districts show up most often in multiple-choice questions asking you to predict consequences of electoral rules. Common stems include how the UK's SMD system affects third parties compared to the two dominant parties, and why proportional representation produces more parties in a legislature than SMD does (the answer hinges on winner-take-all districts wasting votes for smaller parties). Nigeria-based questions also test whether you can connect its legislative structure and districting to representation by population. For free-response questions, this term is comparison gold. Be ready to explain how the UK, Nigeria, and Iran each use single-member districts differently, and to argue how SMD rules cause two-party dominance while PR encourages multiparty systems. The skill being tested is always the same one. Don't just define the system, explain what it does to parties and representation.
These overlap so much that people use them interchangeably, but they answer different questions. SMD describes the district structure (one representative per district). FPTP describes the winning rule (whoever gets the most votes wins, even without a majority). The UK uses both together. Iran shows the difference: its Majles uses single-member districts, but a candidate may need a second round of voting to win, so it's SMD without pure FPTP.
A single-member district system elects exactly one representative per geographic district, so each race has one winner and everyone who voted for someone else gets no seat from it.
SMD systems advantage large parties and tend to produce two-party dominance, because small parties can win meaningful vote shares without ever winning a single district.
The UK and Nigeria use single-member districts for their legislatures, making them the go-to course-country examples for SMD effects.
Iran's Majles uses both single-member and multimember districts, sometimes with a second round of voting, and the Guardian Council vets all candidates before elections (DEM-2.A.1).
SMD is not the same thing as first-past-the-post. SMD is the district structure; FPTP is the plurality winning rule that often, but not always, operates inside it.
On the exam, the key move is connecting electoral rules to outcomes, like explaining why SMD shrinks the party system while proportional representation expands it.
It's an electoral system where each geographic district elects exactly one representative to the legislature. Because each race has a single winner, the system favors large parties and pushes toward two-party dominance, as in the UK and Nigeria.
No, though they usually travel together. SMD means one seat per district; FPTP means winning with a plurality. Iran uses single-member districts for some Majles seats but sometimes requires a second round of voting, which is SMD without FPTP.
Because only the district winner gets a seat, a third party can take 15-20% of the vote everywhere and still win almost nothing. Voters then strategically abandon small parties, reinforcing the two big ones. This is exactly the UK third-party effect the AP exam asks about.
The UK elects the entire House of Commons through single-member districts with first-past-the-post. Nigeria uses single-member districts for its legislature. Iran's Majles uses a mix of single-member and multimember districts, sometimes with runoff voting.
SMD gives one seat per district to one winner, so seat shares can wildly mismatch vote shares. Proportional representation allocates seats to parties roughly in line with their national vote percentage, which lets smaller parties into the legislature and produces multiparty systems.
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