1. Rossen Trendafilov, Fordham U.
Geology versus Agglomeration: Bedrock Depth and the Formation of the Manhattan Skyline,
Jason Barr, Rutgers U.
Troy Tassier, Fordham U.
Rossen Trendafilov, Fordham U.

3. Outline of Talk The “Debate”: Bedrock or not? Manhattan: Simple Model
Video Clip
Manhattan:
Skyscrapers:
Geology and geography
The “Great Leap”
Simple Model
Bedrock’s Effect on Costs
Bedrock’s Effect on Spatial Distribution of Skyscrapers

4. Causation or Correlation?
“[N]ear New York University, the surface bedrock drops appreciably—up to several hundred feet below the street level. Farther south…it comes again to within about one hundred feet of the surface. Diving Manhattan into the ‘downtown’ and ‘midtown’ districts….That is to say, the skyscrapers of New York City are clustered together into the midtown group, where the bedrock is within several feet of the surface, and the downtown group, where the bedrock again reappears to within forty feet of the surface near Wall Street. In any event, it is readily seen how clearly the accessibility of the bedrock has, to some degree, controlled the architectural planning of the city.”
From The Geology of New York City and Environs, C. J. Schuberth © 1968, pps Emphasis added by me.

5. Bedrock Effect Hypotheses
H1: Insurmountable barrier after some depth (Hard technological constraint).
H2: Economically not viable after some point (Economic constraint).
H3: Tipping Point Effect: Small dips have large effects on spatial patterns.
H4: Little or No Effect

6. Alternative Hypotheses
Readjustment to new spatial equilibrium: “Edge City” formation.
Population Movement.
Factory and Slum “flight.”
Transportation Hubs.
Other Economic Factors.

7. Manhattan Geology

8. Manhattan Skyscrapers and Non-skyscrapers (1915)

9. Depth to Bedrock (1915)

10. Building Heights and Bedrock Depths Relative to Street Level

11. The “Great Leap”: Location of Skyscrapers over Time

12. Population Movement: Manhattan Residents above 40th Street

13. Demographic Locations, 1890

14. The El’s (1890): # El’s w/in ½ mile radius of each lot

15. Demand for Height
Office-based firms profits:
FOC:

16. Supply of Height
Profit of Suppliers
FOC:

17. Equilibrium Height h* s.t. 
where A(j) are “centripetal” and “centrifugal” forces; c(j) is the cost of construction.

18. Costs
where

19. Benefit “Gap” Define If BG>0 skyscraper will be built.
In “valley,” depends on slope of valley and additional foundation costs.

20. Benefit “Gap” r(j)-g(hbar) Benefit “Gap” Bedrock Costs for Skyscraper
Distance from Center

21. Agglom. Benefits Large, Bedrock Costs Larger

22. Construction Cost Data
Fuller Construction Company
53 large commercial projects in Manhattan,
Data Collected:
Total Construction Costs
Depth to Bedrock
Building Height
Building Volume
Index of Brick Costs

23. Construction Costs Descriptive Stats.

24. Regression Results

25. Cost Effects
Bedrock costs not relevant (even negative) for smaller projects
For larger projects, only a small fraction of total building costs.
For median skyscraper (21 stories), additional meter down increases costs by about $650 per meter.
32 story building increases construction costs by about $9,000 for each additional meter of bedrock depth (7%).
A 1 st. dev. change in depth to bedrock from the average adds about ½%.

26. Spatial Distribution: Data
Skyscrapers: skyscraperpage.com & emporis.com
Non-skyscrapers: randomly chosen lots.
Heights checked against 1921 Land Book for Manhattan.
Bedrock: (1) Boring maps, (2) USGS contour maps.
Population and Worker Density: Federal and State Censuses.
Land Values and Assessed Values: Reports from the Tax Commissioners of NYC.
Elevated Trains: El Maps from 1890.
Demographics: 1890 Census.

27. Spatial Distribution: Descriptive Statistics

29. Sanitation Districts, 1890

30. Probit Results: Marginal effects on prob
Probit Results: Marginal effects on prob. of skyscraper on given plot of land

31. Relative Effects

34. Predicted Prob. of Skyscraper vs
Predicted Prob. of Skyscraper vs. Latitude for Full Regression and One with Only Bedrock Above and Below Sea Level

35. Conclusions H1: Insurmountable barrier after some depth.
Refuted by scatter plot.
H2: Economically not viable after some point
Refuted by cost regressions.
H3: Tipping Point Effect
Refuted by predicted skyline based on holding bedrock constant.
H4: Little or No Effect.
Consistent with regressions and predicted skyline.

36. Conclusions
Depth to bedrock appears to have had, at best, a modest effect on the distribution of skyscrapers.
Its effect was small relative to the effect of:
Transportation hubs.
Agglomeration benefits.
Avoidance of dense residential and manufacturing districts.
Readjustment to be near white collar workers.