Once erected, Obelisks will enhance all buildings within a certain radius around them—like one huge accessory!
Each Obelisk has a unique effect and range. Every building that's within at least one cell of the Obelisk's range will get all of its benefits, regardless of distance or the number of neighboring buildings.
There are no restrictions on the number of buildings that can be enhanced: place Obelisks to maximize benefit for all buildings within range!
Note that the effects of Obelisks of the same type don't stack: if you place a building within the range of two identical Obelisks, only one effect will apply to the building (the one with the higher value).