They are things you might see from a train. If the train has been moving through open countryside, they are things you might see as you approach a city. "Switches" and "semaphores" relate specifically to trains. Sometimes a set of rails forks or splits into two. The train can go either way. The "switch" is the machinery that controls which way the train will go. A "semaphore" is a kind of traffic light used on railroads. In addition to colored light, it also has a signal arm that might be raised or lowered. A "housing development" isn't directly related to trains. It means a large group of houses or apartment buildings that were all built at about the same time, as part of one big project. In a housing development, the buildings might all look almost the same.