By the mid-game, the number of buildings in the UI gets nearly unmanageable. However, many of those buildings are upgrades of previous buildings.
Imagine if Blast Furnace II was positioned just above and behind Blast Furnace I. This would result in only a slight vertical increase in the size of the UI bar, while still showing the structure clearly. Done for all the buildings with higher-level versions, it would cut the horizontal space taken up nearly in half, meaning that all the metalurgy buildings would be on the screen at once.
