EXTRA3 What points does the professor make about the lightbulbs used in the first generation of skyscrapers? Click on 2 answers.

[00:00.00]Narrator:Recent discussing different factors that influence the development of cities in the United States.
[00:10.10]Lecturer:Today, we’re going to look at New York City, specifically Manhattan. [00:16.22]Now, in Manhattan, two financial districts emerge. [00:20.55]One, in what’s known as Downtown, in the Southern part of Manhattan, and the other, further North, in Midtown. [00:29.29]Many skyscrapers were built in these two areas, and people have typically thought that developers chose these locations because of the geology of Manhattan. [00:41.86]Uh, a group of researchers now suggest, that other economic and social factors were more important in determining which skyscrapers were built, than any geological considerations. [00:54.94]Before we begin, I should mention we’re talking about the first generation of skyscrapers in Manhattan, those built from around 1890s to 1915, between zoning laws were implemented. [01:01.44]So, let’s talk about Manhattan geology and the importance of bedrock. [01:15.74]Bedrock is solid rock, that’s usually buried underneath a layer of soil covering the Earth’s surface. [01:23.95]So, normally you can’t see bedrock unless you dig down to it. [01:28.90]Now, there are certain places in the world, Manhattan Central Park is one, when you can actually see exposed bedrock. [01:38.30]If you visit Central Park, you’ll notice these outcrops of bedrock. [01:43.20]But, throughout other parts of Manhattan, the bedrock gets very significantly, the um, amount of soil covering it changes, depending on your location. [01:55.25]So, Paul, how is bedrock related to skyscrapers?
[01:59.74]Student:Maybe they need to be connected. [02:03.58]Fastened to bedrock for stability?
[02:06.02]Lecturer:Right! [02:07.46]Securing a skyscraper to bedrock helps ensure its stability. [02:12.22]Now, there are costs, and difficulties associated with digging for bedrock. [02:18.31]So, it’s logical for a developer to choose a location with shallow bedrock. [02:24.41]Bedrock that’s close to the surface right. [02:27.91]This usually saves time and money. [02:30.70]So, it’s believed that developers avoided building skyscrapers in areas with deep bedrock to avoid the additional difficulty and expense. [02:40.68]The two areas that emerged as financial districts with many skyscrapers, Midtown and Downtown have shallow bedrock. [02:50.62]So, it’s assumed that bedrock depth was the main factor in determining their location. [02:56.95]But, this is being challenged. [02:59.40]Any idea why? Jennifer. 
[03:01.27]Jennifer:There are other factors right? [03:04.10]I mean, there are lots of costs associated with building skyscrapers other than just construction costs. [03:12.22]Like, what about the cost of buying the land?
[03:15.62]Lecturer:That’s true, and in this study, the researchers discuss that. [03:19.90]Back then, land was more valuable in Midtown and Downtown, where the bedrock’s shallow, than in the area between these two locations, where there’s deep bedrock. [03:31.31]So, if saving money was the main consideration, it actually would have been cheaper to build the skyscraper where the bedrock was deep - because the cost of land in that area was far less than in areas with shallow bedrock. [03:46.39]Any extra cost associated with digging to the bedrock, would be canceled out by lower land cost, and, some skyscrapers were developed in this area, like, the New York World Building - which was built above bedrock buried 45 metres below the surface. [04:05.59]So, if bedrock depth was the main consideration for developers, we wouldn’t expect to see any skyscrapers in areas like this. [04:15.29]But, why were developers willing to build skyscrapers in Midtown and Downtown, where land acquisition costs were higher? [04:24.55]Well, they probably thought they’d profit more from building skyscrapers in areas where businesses were already established. [04:34.27]This research suggests that the location was likely based more on social and economic factors. [04:41.90]Things like - proximity to transportation, and elements of the neighborhoods already in place! [04:48.48]These researchers analyze data and perform what’s called a probit analysis. [04:55.00]I don’t want to spend time discussing the research method, but, I’d like to discuss their findings. [05:01.25]One factor influencing a skyscrapers’ location, seems to have been proximity to public transportation.[05:09.14] We researchers calculated the numbers of railway stops within a half-mile radius, and it seems developers were sensitive to this! [05:18.70]Another factor developers had to consider then, which they might not today, is the amount of natural light buildings would receive. [05:27.77]These early skyscrapers had to rely on sunlight, because the light bulbs back then didn’t give off much light. [05:35.69]And, you know, if too many light bulbs were used, the room’s temperature would increase quite a bit! [05:42.26]This was problematic when the weather was hot, so, adequate sunlight, was important.