CIG - Turning Data into Information Using ArcGIS 10
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urning Data into Information Using ArcGIS 10
MÓDULO 1
Representing geography
In order to build a representation of any part of it, you must make choices about what to represent, at what level of detail, and over what time period.
What are geographic data?
Geographic data link place, time, and attributes.
Place
Place, or location, is essential in a geographic information system. Locations are the basis for many of the benefits of geographic information systems: the ability to map, to link different kinds of information because they refer to the same place, and to measure distances and areas. Without locations, data are said to be "aspatial" and have no value at all within a geographic information system.
Time
Time is an optional element. Many aspects of the earth's surface are slow to change and can be thought of as unchanging. Height above sea level changes slowly because of erosion and movements of the earth's crust, but these processes operate on scales of hundreds or thousands of years, and for most applications (except geophysics) we can safely omit time from the representation of elevation. On the other hand, atmospheric temperature changes daily, and dramatic changes sometimes occur in minutes with the passage of a cold front or thunderstorm, so time is distinctly important. Attributes
Attributes refer to descriptive information. The range of attributes in geographic information is vast. Some attributes are physical or environmental in nature (such as atmospheric temperature or elevation), while others are social or economic (such as population or income). There are five main types of attributes: nominal, ordinal, interval, ratio, and cyclic:
The simplest type of attribute, called nominal, is one that identifies or distinguishes one entity from another. Place names are a good example, as are addresses of houses and the numbers on a driver's license—each serves only to distinguish the incidence of
urning Data into Information Using ArcGIS 10
MÓDULO 1
Representing geography
In order to build a representation of any part of it, you must make choices about what to represent, at what level of detail, and over what time period.
What are geographic data?
Geographic data link place, time, and attributes.
Place
Place, or location, is essential in a geographic information system. Locations are the basis for many of the benefits of geographic information systems: the ability to map, to link different kinds of information because they refer to the same place, and to measure distances and areas. Without locations, data are said to be "aspatial" and have no value at all within a geographic information system.
Time
Time is an optional element. Many aspects of the earth's surface are slow to change and can be thought of as unchanging. Height above sea level changes slowly because of erosion and movements of the earth's crust, but these processes operate on scales of hundreds or thousands of years, and for most applications (except geophysics) we can safely omit time from the representation of elevation. On the other hand, atmospheric temperature changes daily, and dramatic changes sometimes occur in minutes with the passage of a cold front or thunderstorm, so time is distinctly important. Attributes
Attributes refer to descriptive information. The range of attributes in geographic information is vast. Some attributes are physical or environmental in nature (such as atmospheric temperature or elevation), while others are social or economic (such as population or income). There are five main types of attributes: nominal, ordinal, interval, ratio, and cyclic:
The simplest type of attribute, called nominal, is one that identifies or distinguishes one entity from another. Place names are a good example, as are addresses of houses and the numbers on a driver's license—each serves only to distinguish the incidence of