Every major north american city has a legacy telco central office in downtown, in a very central location, from the days of pulse-dial and then DTMF dial analog phones. Always owned by whatever corporate entity the Bell System and then ILEC eventually became.
Yeah, you have to remember that in pulse dial days a central office station had a reach of roughly 3 miles. The longer you go, the more you're paying for cable, repeaters, or just losing quality. 90 volt AC for ringing has a limited range!
> How do they colour-code the wires to identify them?
It’s actually pretty simple. There are only 10 colors: blue, orange, green, brown, slate, white, red, black, yellow, and violet. They’re grouped in “binders” (using colored strings). You’re likely familiar with the first four pairs from network cables (which omit the white/slate pair). After cylcling through blue through slate paired with white through violet (25 pairs), the wires are bundled with binders starting with blue/white string. That gets you to 625 pairs (the first picture posted above is 600 or 625 pairs). After that, the binder groups are bound in a similar fashion (typically if you’re going beyond 625, the slate/violet binder is omitted to get a nice round 600 in the first group).
100-pair cable is only about 3/4” diameter. I have a 24-line 1A2 telephone that uses 75 pairs just to connect to the phone switch and two 100-pair cables feeding a telephone display case in my living room.
It takes me about a half hour to punch down 100 pairs on a 66-block. Old school telecom guys could probably do it in under 10 minutes.
Seattle, for example, also has the Elliot CO in Belltown: http://www.co-buildings.com/wa/206/