“A city is not a tree”
PAPER X — DESIGN · QUESTION 7 OF 40
In plain terms: The free classic essay containing the mathematics — why planned cities simplify overlap that living cities keep.
The question as set
“A city is not a tree.” State the mathematical distinction Alexander drew — tree against semilattice — and say whether it settles whether a city can be designed.
The question in Paper X · Its section on the reference page
The question in context
This is question 7 of the 40 set in Paper X — Design of The Truly Hardest Exam in the World, the examination of The College of All Minds. In the College’s subject index it is filed under Cities and settlement and Maps and representation. Like every question of the College, it carries three references of record, verified live at publication and described twice — technically, and in plain terms — so the ground can be judged before it is walked. The response required is an argument, not a survey, of at most three thousand words, as technical as the question demands and no more.
The references of record
The distinction itself: tree versus semilattice as overlap structures, with the designed city convicted of treeness.
In plain terms: The free classic essay containing the mathematics — why planned cities simplify overlap that living cities keep.
The kind of problem named: organised complexity — the class Jacobs assigned cities to when she pressed the case on the planners.
In plain terms: The free classic that first named the sort of problem a city is; Jacobs built her famous last chapter on it.
Cities as complex systems: scaling, interaction, networks, dynamics
The modern formalisation: scaling, networks, and morphology — what “can a city be designed” means when cities are grown systems.
In plain terms: The free survey by the leading urban modeller, updating Alexander’s structures with today’s data and mathematics.
Background: A City is Not a Tree · Semilattice