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Discussion Starter · #1 · (Edited)
I wasn't sure whether to put this on the skyscraper forum or this forum, but as this is related to just construction in general I'll post it here for now.

A while ago I thought about a way to measure the size of a skyline empirically and objectively, quite similar to the "skyline ranking" point system used on Emporis. I wanted to also see the history of those points over time, but as Emporis only provides the top 100 cities and only shows the current points a city has (the Wayback Machine only goes as far back as 2011), I wanted to determine the growth of a city (and its skyline) over time.

My other issue with the Emporis point system was that the points assigned to each building are quite arbitrary, with a 19 floor building obtaining 1 point but a 20-story building having 5. My point system is also based on floor count, as height information is not available for every building, which I'll explain below.

For any city, only buildings with 10 stories or more are counted in the point system. Since a building's height has a disproportionate impact on the city's skyline, the points awarded for a building increase faster than the number of floors. This increase is reflected in Emporis's point system as well. The rate of increase is somewhat arbitrary, but to make it close to Emporis's ranking as possible, I've decided that a 10-story building would merit 1 point.

The point system is calculated by the formula:

Points: (number of floors^2.5)/(10^2.5).

So a 20-story building would have 5.65 points, and a 100-story building would have ~316 points. I know that using floor instead of height is a compromise I had to make to obtain more data. Now, with Emporis' extensive database, and others from skyscrapercenter.com, I can calculate the points for any given skyline, and the growth of a city's number of points.

As it takes a long time to gather the data for a single city, I've so far only done a handful of British and American cities, but I think the data I've gathered may be interesting. I decided to do American cities first since they have had the longest history of skyscraper construction. Any other city outside of the US or Western Europe would see all see a concurrent increase in points starting from the 1990s until now, which is less interesting to visualize.

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The Y-axis quantity is points; here we can see the skyline growth rate of 8 cities over time until 2020, including those under construction (before the impact of COVID-19) with Emporis data. For maximum accuracy, I included demolished buildings whose points only counted at the time when they existed. Cities whose year of construction or demolition are unknown were not counted, and would make a miniscule amount of difference on the chart. To be honest, not counting demolished buildings would not make a significant difference for most US cities, but for accuracy's sake I did anyway.

Using the point system as a proxy for skyline size, this graph would mean that Miami has only recently reached a skyline size Chicago had in 1972, and is the 3rd largest skyline in the U.S. I had to cut Chicago off because if I included it to its current extent the graph would look like this (and the other cities would be hard to make out):

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Meaning Chicago just dwarfs every other skyline in the US save for New York. Speaking of New York, it would take a long time to calculate the data, so I'm not going to do it too soon, but I predict it'll dwarf Chicago when its done. We can see some interesting trends in both graphs, especially the lulls in construction. Most visible is the impact of the Great Depression and WWII, which affected construction for 3 whole decades (1930s to 1950s) before it picked up again. The other break is in the beginning of the 1990s , although I'm not too sure why. If you guys can find any more interesting facts, feel free to share it in this thread!

Alright, that's all for now. I'm gonna to this to a lot of other cities soon, just to see their skyline growth over time. Here's the above graph in logarithmic scale, so the pre-Great Depression construction boom can be better shown:
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