Geography Reference
In-Depth Information
Like Gridville, the world as a whole possesses a grid whose coordinates may be used to identi-
fy the absolute location of things. Indeed, that is why a Greek named Hipparchus invented the
global grid some 2,200 years ago.
As chief librarian at the great library in Alexandria, Egypt, Hipparchus compiled information about
lands and cities all over the expanding Greek world. He saw the value of accurately locating objects
on a map, but in those days that was easier said than done. Maps were notoriously inaccurate, due in
good measure to lack of a systematic means of stating the location of things. So Hipparchus set out to
rectify the situation, and came up with the global grid that is still in use today (see Figure 3-2).
Avoiding gridlock
Proper use of a grid coordinate system to state the absolute locations of things depends on a
handful of prerequisites. Think of these as ways of avoiding gridlock:
Familiarity breeds success.
Knowledge of the naming and numbering of grid components
is essential. If, for example, that stranger were not familiar with Gridville's grid, then telling
her the hospital is at “the intersection of South 1st Street and West 1st Avenue” would have
made no sense whatsoever. The same is true with respect to the global grid. That is, knowing
how the lines are named and numbered is essential if you are to use the grid successfully.
Unique components.
Each road in Gridville and each line on the global grid must have a
unique name. In Gridville, for example, there must be only one road named South 1st Street,
and only one named East 1st Avenue. If multiples exist, then more than one site could satisfy
“the intersection of South 1st Street and East 1st Avenue.” And that would rather defeat the
concept of absolute location, whether in Gridville or around the globe.
No double-crossing allowed.
Don't take that as a threat or accusation. What I mean is two
roads in Gridville may cross each other only once. The same goes for two lines on the global
grid. If they have multiple junctions then, such as the last point, there would be two or more
intersections of, say, South 1st Street and East 1st Avenue. And again, that would defeat the
concept of absolute location.
