Going off on a historical tangent, which is something I quite often do, I was reading only the other day that when Edinburgh Corporation Transport became Lothian Region Transport in 1975, they ran quite a number of "circle" services, which went around the city centre but not through it. As the name suggests, they ran in a circular manner, without a terminus at either end (although some were more of a figure of 8). There was an old joke about lost tourists who couldn't find "Circle" on their Edinburgh guide maps despite all the buses going there. The 1 and the 6 used to run as circles, one going one way and one going the other. At one point the 2 and 12 were also circular compliments.
Anyway, sooner or later, LRT got a load of staff in at the top (including quite a few from Eastern Scottish / SMT) who didn't like circular routes and most of them were disposed of and the remnants retained as less important routes, with lighter service patterns and single deckers.
A good part of the core of the current Lothian Buses route structure is basically just the old Edinburgh Corporation Tramways routes, but extended further out at either end to account for the growing city. Trams ran numbers 1 - 28 and 15 of these ran along Princes Street, with a further 3 I think taking George Street. When they got rid of the trams, there was a problem as the Corporation buses also ran numbers from 1 and up. So, when a tram service was replaced with a bus, it kept the number of the old tram route and 30 was added to the pre-existing bus route of the same number so that there were no conflicts. Not all the tram routes were directly replaced so sometimes there was no need to renumber the bus.
When you compare the old tramways map with current bus route map, routes 4, 5, 7, 8, 11, 12, 13, 15, 16, 22, 23, 25, 26 and 27 are pretty faithful to the old tram routes they replaced, with little in the way of deviation in the centre of the city, but expanded further out at either end to serve the expansion of the city since the 1950s. Some of those tram routes were laid down in the 1880s, so we have a transport network that still owes a lot to Victorian planning, given it was original a cable-hauled system, one of these practicalities was running near the winding station at some point (which existed at Shrubhill, Tollcross, Henderson Row and Portobello).