Geography Reference
In-Depth Information
Certainly in this age—early in the twenty-first century, when what computers do seems indistinguishable
from magic—it is difficult to remember or believe that a computer is, at its heart, a conceptually simple
device. The way in which it is simple has a profound impact on its use for GIS. Further, the simplicity
imposes constraints on what we can do.
The elementary nature of a computer is based the idea that just the existence or nonexistence of a
single thing, when put together with other such things, can be a powerful mechanism for representing
meaning—a code, if you will, consisting of 1s and 0s. In the case of Paul Revere's Ride, the things were
lit lanterns—two of them hanging in a belfry arch. If a lamp burned we could call that a “1.” If not, a “0.”
Therefore, the code was as follows:
00:
No British
10 (or 01):
British by Land
11:
British by Sea
As for the other definition of information—a small amount of matter-energy with the potential to
produce large effects—it's pretty clear, if the poem can be believed, that in some sense the United States
was saved that night. The beginning of the battle has been described as “the shot heard round the world.”
Computer Hardware—What a Computer Does
The information in this section is intended to demystify computers for you. As computer power
increases—with abilities like speech and facial recognition and championship chess playing—the tendency
is to regard a computer as basically incomprehensible. Since the fundamental logical structure behind
the operation of a computer is quite simple, I believe such understanding should be part of a student's
knowledge base. It's not that hard, and you may find it interesting. And the knowledge may help you to
figure out why things go wrong sometime when you are using a computer to work on a GIS project.
A refresher: All the operations of a computer are based on the concept that combinations of binary states
can represent information. Binary states can be: on or off; A or B; tied or untied; yes or no; exists or does
not exist. Customarily, we represent those two states by BInary digiTS (BITS). With these a computer does
three things:
Strings of 0s and 1s are fed in (input) to the machine and placed electronically into a “store” or
“memory.”
❏
Bits from the store are manipulated according to a number of exact rules (operations of arithmetic
making up a good-sized subset of those rules), and the results of those manipulations are placed
back into the store.
❏
Strings of 0s and 1s are sent out from the store to output devices.
❏
That's it! Everything else is simply elaboration on this basic theme.
Why binary states? Because, in the physical world, it is easier to identify the existence (1) or nonexistence
(0) of something than it is to identify the degree to which something is present. For example, it is easy to
tell by looking at a light bulb whether the switch that feeds the light bulb is on or off (i.e., whether the
switch that controls it is set to 1 or 0). It is not so easy to tell, by looking at the brightness of a bulb, the
position (say, 1, 2, 3, or 4) to which a light bulb dimmer (rheostat) is set.
Search WWH ::
Custom Search