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human
How are underwater cables laid? Plus other related questions in the text.

I understand that This has occurred since the days of the telegraph and now with the internet and so on. But I wondered how the process laying the wires is undertaken. What do the wires look like, is there protections against marine life, pressure, conditions down there. 

Do they wear out? Is maintenance done? How are they upgraded/replaced?

What determines the best location for the routes? Is it simply shortest distance? Is there any consideration of the layout of the seabed or anything like that. 

How do people know they are in the right place? What are the costs of these operations? Are there companies which specialise in underwater cabling? Does there have to be special political permission between countries where the wires connect and the waters they cross? etc etc. 

Infographics would be greatly appreciated as well. 

Thanks.
gpt
Seabed cables and pipelines are very complex, and to answer all the questions you've asked would take the better part of a 100+ page technical report. 


In short, cables are typically manufactured in protective, elastic sheathes, designed for the operations conditions (depth, etc) and deployed by spool from the back of a ship, generally with some subsea monitoring (ROVs, divers etc.) Typically many spools would be required, so each cable is attached to the previous on in situ, before being rolled off into the ocean. 


In some circumstances they are buried to protect from seabed scouring, or other potential damaging items (anchors for example).

Maintenance or retrieval would be more expensive (in most cases) than replacement. 

Politics are important. Each country owns a set distance of seabed from the coast line, and international agreements/treaties/permits are required. 


Routing is done via economics. The cheapest solution is usually the one chosen. However this may be impacted by the need to bury the lines, and operational requirement for deploying the cable(s). 


Deployment is done via GPS, and yes, they are crazy expensive. You need specialized ships for often months at a time. Chartering ships gets you into the millions of dollars pretty fast, never mind manufacturing costs  and required technical expertise on board. Add in the time/man hours you need to complete the design, approve all the permits and get the ball rolling. Weather can impact operations significantly, so you need to account for scheduling risk etc. etc. etc. 


TL;DR: Subsea cables are laid very carefully.