Sure, simple math imagine a country with five “districts.”
Let’s assume the constitution mandates that districts be as close as possible in population size and “maximum geographic compactness.” [While not the only concept of a fairly drawn district, it does have some traction in States that have attempted to make district non-partisan and among algorithm makers and geographers somewhat relevant Slate article]
Let’s also say that there are two parties, the “People’s Party” and the “Citizen’s Party.” Let’s say in American political parlance the People’s Party is “liberal” and the Citizen’s “conservative.”
In two of the districts, District 1 and District 2, there are large (for this small country) cities. They have large minority populations, young unmarried people, college students and professors and basically many of the traditional groups that would vote Democrat in the United States.
Districts 3, 4, and 5 are more suburban or rural, more from the majority race, more older married couples, more religious people etc. Basically groups that vote more Republican in the United States.
Alright, so each District has 100,000 residents. District 1 and 2 are very small, because they center on the country’s only two large cities, and under the concept of geographic compactness there is no way to avoid this.
So in an election the break down comes down to:
District 1: 100,000 votes - 90% People’s Party, 10% Citizens
District 2: 100,000 votes - 90% People’s Party, 10% Citizens
District 3: 100,000 votes - 30% People’s Party, 70% Citizens
District 4: 100,000 votes - 40% People’s Party, 60% Citizens
District 5: 100,000 votes - 45% People’s Party, 55% Citizens
So in total, the People’s Party wins two districts and 295,000 voters preferred a candidate from the People’s Party. The Citizen’s Party wins three districts, and 205,000 voters preferred a candidate from the Citizen’s Party.
In a fictional country with two cities that are almost the size of a district, and with the district guidelines above it would be very, very hard to “fix” the “disadvantage” that the People’s Party has because of their extreme concentration of voters. Basically, people who identify with that party have chosen to collect in a manner that isn’t an even distribution around the country and that has electoral negatives for them. I’m not 100% sure how you fix that with a single member district system that has first past the post voting without basically saying “well, this is the majority party in overall votes so we will just draw the districts to make sure they win all 5.”
That may “feel” right to someone that thinks whichever party has the most votes should be in power, but it would seem to violate the concept of non-partisan and “fair” district drawing. (A very hard to define thing, the concept of geographic compactness is suggested as a fair drawing technique, but there is no true objective fairness and most people define fair to equate to what benefits their party the most.) The truth is if you choose a single member district system with first past the post voting unless parties have voters perfectly evenly distributed throughout the country I am not 100% sure how you can avoid situations like I’ve outlined in this ‘extreme worst case’ scenario above. Even in the UK which almost everyone agrees is not intentionally gerrymandered, there have been arguments made that differing geographic concentrations of voters have created “undesirable” differences between national popular vote and the party that ends up winning overall.