Even though Urban area has longest buildings, but the Mobile or Cell Phone towers are short comparing to the towers in Rural area.
What is the reason for this?
Mobile phone towers typically called as Base Station covers a certain area.
Each base station is limited to handle number of simultaneous connections (i.e, number of mobile phone users).
In Urban Area, more number of mobile phone users may exist. To handle more number of users there is need for more number of Base stations. Also, to avoid interference between the towers (base stations) it is constructed as short.