Not all the towers along a transmission line are identical. Look closely at a tower where the line makes a sharp turn and you will likely find it is wider and beefier than other towers along the route. The added strength and weight are needed to resist the unbalanced pull of the conductors, which might overturn an ordinary tower. These special towers are called deviation or angle towers.
The transmission-line tower everybody knows is an Erector Set latticework of steel girders and diagonal braces. The techniques for designing and building these towers are the same ones used in constructing steel bridge trusses or crane booms. The individual pieces can be made cheaply from rolled steel and then bolted together on the site. This last point is more important than it might seem: transporting a fully assembled tower 100 feet tall is an awkward and expensive business.
It seems this transformation, from physical object to vector of data, is a general and oft-repeated process in the history of technology, where new inventions begin in an early experimental phase in which they are treated and behave as singular individual things, but then evolve into vectors in a diffuse and regimented system as the technology advances and becomes standardized.
In the early history of aviation, airplanes were just airplanes, and each time a plane landed or crashed was a singular event. Today, I am told by airline-industry insiders, if you are a billionaire interested in starting your own airline, it is far easier to procure leases for actual physical airplanes, than it is to obtain approval for a new flight route. Making the individual thing fly is not a problem; inserting it into the system of flight, getting its data relayed to the ATC towers and to flightaware.com, is.