Geography Reference
In-Depth Information
CHAPTER
2
OVERVIEW
IN WHICH you look at a variety of
geographic datasets involving
vector, raster, triangulated irregular
networks, and terrains. Datasets of
shapefiles and geodatabases are
considered, and you are introduced
to Esri's ArcMap.
Characteristics and
Examples of Spatial Data
The Original Form of Spatial
Data: Maps
Thirty years ago spatial data meant maps. A single map is a
spatial database and, for many purposes, a very good one.
For hundreds, perhaps thousands, of years, almost all of
the information used to support land-related planning and
management, and myriad other activities such as navigation,
has come from maps. Mapmaking became a well-developed
activity. The piece of paper on which the map is drawn is
a continuum that can represent the quasi-two-dimensional
surface of the Earth in an obvious way. (“A picture is worth a
thousand words.”) Many times when people are asked “How
do I get to . . . ?” they respond, “Let me draw you a map.”
Why, then, should we spend millions of dollars on databases
composed of discrete symbols when maps are available?
Among the answers are that maps alone are extremely hard
to use for many of the analyses that human activity requires.
There are precious few ways to combine graphic information
with other graphic information. Decisions involving the space
we live in are becoming more difficult all the time because of
the larger number of factors that must be considered. Physical
techniques have been evolved for combining maps, such as
overlaying one transparent map with another and looking
through the composite, but these methods are tremendously
time-consuming and have substantial limitations in terms of
useful output.
The reason spatial databases composed of discrete symbols
(numbers, letters, and special characters) are overtaking map
use is that, in the last 30 years, we have learned a great deal
about handling discrete symbols, and we have developed both
techniques and equipment (primarily digital computers and
software) that can manipulate symbols efficiently and quickly.
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