The main reason why these changes have happened is that over time, the city has grown, and land value has increased. This pattern is studied by what is known as gradient analysis. Gradient analysis measures the changes in land values and population density from the city center outwards.
In an HIC city like the one in the example, the population in the CBD initially increases, until land value becomes too high for a lot of people, which leads them to move outwards, decreasing the population in the CBD. As more people from the CBD move to the HIC inner-city residential zones, the population begins to increase. The same process as the one in the CBD is repeated, and the population in these areas decreases as well, as people move outwardly again.
