When you vote in the upcoming election, you may not be voting in the same district as you did previously. You can thank the founding fathers for that. They reasoned that with every population shift in the US, voting district borders should be redrawn to prevent bias towards a particular voting block. At least, that was the general idea. However, as early as our first elections, some of those same men realized that this tool for balance, could equally be re-tooled for partisanship. So if the district next to yours saw a shift, but yours did not, it may still be redrawn in an effort to maintain or change the voting block next door. Since most states have redistricting committees determined by the majority party, they are often biased in favor of keeping incumbents in their seats.
One of the first to utilize redistricting to this effect was Elbridge Gerry, a signatory of the Declaration of Independence but not the Constitution (he abstained because of the lack of a Bill of Rights). His redistricting was so skewed, that on a map it looked like a slightly misshapen salamander. Seeing the political fodder, his opponents branded the practice of biased redistricting as Gerry-Mander-ing, a label so sticky (like a salamanders grip) it has survived to this day. Talk about bad PR... Since then, various cases on gerrymandering have been brought to the courts, and some legislation has been passed. Some states now have nonpartisan or bi-partisan committees to redraw district lines. However it is too soon to tell if that is enough to prevent the kind of alleged bias the Supreme Court will hear in the first case on gerrymandering to make it to SCOTUS in over a decade.