Urban consolidation is when cities get bigger and bigger without expanding outward to take up more land. Instead of building new roads and neighborhoods elsewhere, people build more apartment buildings and skyscrapers in the city center.
Think of it like a pizza. When you cut a pizza, you can either make more slices or make the same number of slices bigger. Urban consolidation is like making the same number of slices bigger instead of making more slices.
There are good things and bad things about urban consolidation. The good thing is that it can help reduce traffic and pollution. If people live closer to their jobs and the places they want to go, they can walk, bike, or take public transportation instead of driving.
But there are also bad things. One problem is that it can be expensive to build high-rise buildings in the city center. This can make housing more expensive and force people to move farther away. Also, some people like having a little more space and may not want to live in an apartment building.