Built systems 173Ber+Chi+Sto+Sop+Edm•Cai*
Phi+Por•Rom+Bei*
Mos*
Lon*
Seo*
Number of primary radial roads extending outward
beyond metro areaNumber of primary radial commuter-rail linesextending outward beyond metro area1246810(^035791113)
Figure 7.4Number of radial commuter-rail lines relative to radial highways
extending from a metropolitan area. Number of commuter-rail lines is determined
based on 16 possible compass directions. All radial roads are multilane and extend
≥20 km beyond the metro-area border. See Figure 7.2 caption.
All regions have a major airport near the city for passenger air travel, and
commonly also for cargo freight. A second major airport provides flexibility if the
nearby one becomes inadequate, or if passengers and cargo are concentrated in
different airports, or if international and local/regional travel is separated. Most
regions probably have a major military airport. Some regions have many airports
(Moscow, London), presumably with different major uses. Some airports may be
decommissioned (Edmonton), but remain conspicuous on the aerial images and
are therefore mapped.
[S10]Most cities have the nearest major airport <20 km from the city center, and most cities
with two or more major airports have the second closest one >20 km distant(Figure7. 6).
The primary airport is close and convenient to the city for passengers and
business cargo, and may be connected to the city by rail. Where the second