The study looked at how the number of apartments in Donghae changed from 1980 to 2001. They surveyed 82 apartment buildings and found that more apartments were built over time, with the most being built in the fourth period. There was a difference in apartment supply between the south and north areas. The study also found that smaller apartment buildings with fewer than 5 stories were continuously built. Overall, the supply of apartments in Donghae was influenced by factors like demographics and housing policies.