Keyspatial attributes 121(7) Flood-hazard area (data not easily obtained, so typically metro-area loca-
tions up to a few meters higher than adjoining rivers or seacoasts are
marked).
(8) Fire-hazard area (data not easily obtained, so typically locations in dry
climates where forest/woodland adjoins built areas are marked).
(9) Airport (includes the primary busy airport for city, other passenger air-
port, military airport, and, in at least one case [Edmonton], a large
decommissioned airport).
(10) Noise of flying aircraft (data not easily obtained, so locations extending
c.3--5 km (2--3 mi) out from major runways [Miller2005]aremarked).
(11) Nearby slopes facing city (covered by natural vegetation, agriculture, or
built area [wealthy to slum], these slopes are of special visual, recre-
ation, erosion, flooding, cooling, air-cleaning, and biodiversity impor-
tance associated with proximity to city).
(12) Market-gardening area for vegetables/fruits near city (sometimes called
truck farming, this area provides low-transportation-cost fresh produce
forcity markets and restaurants [Chapter3], and isoftenthreatened by
development).
(13) End of commuter rail (most radial commuter-rail lines serve the metro
area, but some extend outward to satellite cities and towns [e.g., London,
Philadelphia]).
(14) Commuter residential area (data not easily obtained, so locations are
mostly based on consultations with knowledgeable persons).
(15) Biodiversity area (data not easily obtained, so, as elaborated below, loca-
tions mostly based on parks, natural areas, etc. on published maps, and
on distinctive topographic and landscape ecological patterns).
(16) Wetland (generally rare in urban regions due to drainage and filling).
(17) Salt flat or intermittent lake (intermittent lake seasonally or periodically
dries up, often leaving a salt flat).
(18) Volcano (active or apparently recently so).
(19) Mine site or quarry (for valuable minerals, coal, or sand/gravel; data not
easily obtained; since quarries and most mine sites are usually small,
only large mine sites prominent on images are marked).
(20) Water-supply source (location where water is extracted from a water
body; a few cities depend on groundwater wells or streams, so general
areas are marked).
(21) Drainage area around water supply (without topographic maps in many
cases, the general area seemingly most important for water-supply pro-
tection is marked).