120 Thirty-eight urban regions
(G) Desert/desertified area (desert with <25 cm annual precipitation, some-
times sand-covered, but more typically stony/rocky with sparse low
shrubs and other plants; desertified area overgrazed, eroded, salinized,
and/or water-table-lowered by human activity).
(H) Metropolitan area (the essentially continuous built area including a cen-
tral major city).
(I) Small/medium built area (satellite city or a town; based on area, not
population; villages, hamlets normally not included).
(J) River/major stream (in moist climates typically at least a fourth-order
stream [Wetzel2001]; in dry climates with seasonal surface-water flows,
arelatively wide [typically >30 m] floodwater channel).
(K) Multilane highway (usually a four-lane divided highway; sometimes
more traffic lanes).
(L) Pavedtwo-lane main road (asphalt/tarmac/concrete surface; mapped in
regions with few or no multilane highways outside the metro area).
(M) Unpaved main road (mapped around cities with few or no paved main
roads outside the metro area).
(N) Urban-region boundary (determined as described in the preceding
section; not visible on aerial image).Site types
From several dozen possible spatial attributes considered and partially
mapped, the following 26 types of major sites were considered especially impor-
tant and found to be widespread. The absence of a mapped area or site on an
image usually means it does not exist. In some cases it may exist, but no infor-
mation was located. Although often many small sites exist, only major sites were
mapped.
(1) Dock area for shipping and/or ferry.
(2) Industrial area (usually a group of industries; occasionally a single large
one).
(3) Sewage treatment facility (often only many small ones are present).
(4) Solid-waste disposal (sometimes combined with a recycling facility).
(5) Water-quality poor (data not easily obtained or interpreted, so typically
awaterbody downslope of a city, industrial area, sewage treatment
facility, or mine site ismarked).
(6) Air-quality poor (data not easily obtained or interpreted, so typically
locations in center city and downwind of the city or an industrial area
are marked).