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Fig. 2.5
A Landsat photograph of Britain (
left
). Central London (
right
)isshownasthe
blue
area
near to the lower right corner. The Landsat satellite took the photo on May 23rd, 2001 (Reprinted
Satellites have played an increasingly significant role in making thematic maps.
For example, the LANDSAT 7 satellite, launched in 1999, carried the Enhanced
Thematic Mapper Plus (ETM
C
) instrument, which is an eight-band multispectral
scanning radiometer capable of providing high-resolution image information of
the Earth's surface. It detects spectrally filtered radiation at visible, near-infrared,
short wave, and thermal infrared frequency bands from the Earth. Nominal ground
sample distances or “pixel” sizes are 49 ft (15 m) in the panchromatic band; 98 ft
(30 m) in the 6 visible, near and short-wave infrared bands; and 197 ft (60 m) in the
thermal infrared band. The ETM
C
produces approximately 3.8 gigabits of data for
each scene, which is roughly equivalent to a 430-volume encyclopedias. Figure
2.5
shows a photograph of Britain from LANDSAT and a detailed photograph of Central
London.
2.2
Terrestrial Maps
The Greek astronomer Claudius Ptolemy (c.85-163 AD) generated one of the most
famous world maps in about 150 AD. Unfortunately, none of his maps survived.
Scholars in the Renaissance in the fifteenth century reconstructed Ptolemy's map
following his instructions (See Fig.
2.6
).
Ptolemy's map represented his knowledge of the world. The map was most
detailed round the Mediterranean because he worked in Alexandria. The map
showed only three continents: Europe, Asia and Africa. The sea was colored in
light brown, the rivers in blue, and the mountains in dark brown. The surrounding
heads represent the major winds.
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