Do you know what a boundary is? It's like the line someone draws between two places, like a school's playground and the street outside.
In the United Kingdom, there are groups called "Boundary Commissions" that are responsible for drawing lines between different areas of land, called constituencies. Constituencies are areas where people live and vote for people to represent them in the government.
The Boundary Commissions have to make sure that each constituency has roughly the same number of people living in it. That way, each member of Parliament represents the same number of people and no one is unfairly advantaged or disadvantaged because of where they live.
They also have to consider other things, like natural features such as rivers and mountains, as well as important things like community relationships and local identity.
Once the Boundary Commissions have finished drawing the lines, they present their proposals to Parliament, who then make a decision on whether or not to accept them.