Mapping by computer

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					              Mapping by computer
As the explosion of man’s knowledge continues , one of the
chief problems he faces is to store data in such a way that it
is quickly accessible . In the case of mapping , such data
already exists .Given that it can be stored in on magnetic
tapes and that a computer can be programmed to select the
data required without delay , there is still the problem of
how to store a map outline simply as numbers . The method
used is the obvious one of treating outlines , contour lines
and so on as loci of large numbers of closely neighbouring
lines and giving their x and y coordinates relative to certain
axes. In this way a map is stored as an immensely long list of
x and y coordinates .
Kept on magnetic or paper tape , or punched cards , these
constitute cartographic data banks . The first step in this
method developed at the Royal College of Art in London , is
to convert existing maps into stores of numerical
information .
This process , called ‘digitizing’ , is carried out by a reading
device called a ‘geameter’ , which follows outlines and
contour lines , recording ten points every millimetre , and
converts them into streams of number pairs . In the ‘output’
process , the information is used to activate a scribing pen
which draws out the line required . Speeds of drawing at the
moment are just over six centimetres per second , which
must be greatly increased as the process is is extremely
expensive .

( from M.HOLT & D.T.E. MARJORAM , Mathematics in a
changing world . Heinemann_adapted . )

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