کارتوگرافی(نقشه کشی)-Cartography
Cartography
The techniques concerned with
constructing maps from geographic information. Maps are spatial representations
of the environment. Typically, maps take graphic form, appearing on computer
screens or printed on paper, but they may also take tactile or auditory forms
for the visually impaired. Other representations such as digital files of
locational coordinates or even mental images of the environment are also
sometimes considered to be maps, or virtual maps.
Maps and
uses
Because the environment is complex
and everchanging, the variety of maps and map uses is unlimited. For instance,
maps are indispensable tools for navigating over land, sea, or air. Maps are
effective both in exploiting natural resources and in protecting them. They are
used to investigate geographic phenomena, including environmental pollution,
climate change, even the spread of diseases and the distribution of social
phenomena such as poverty and illiteracy. In addition, maps can be used to
communicate insights derived from geographic research through publication in
periodicals and books and through distribution over computer networks and
broadcast media. Every private business, government agency, and academic
discipline whose products, services, or objects of study are geographically
dispersed benefits from detailed, up-to-date maps. Unfortunately, appropriate
maps often are unavailable.
Map scale and geographic
detail
Maps often include insufficient or
excessive detail for the task at hand. The amount of usable detail on a map
varies with its scale, because human visual acuity and the resolution of
printing and imaging devices are limited. Maps that depict extensive areas in
relatively small spaces are called small-scale maps. For example, on a 1-ft-wide
(30-cm) map of the world, on which the ratio of map distance to ground distance
is approximately 1:125,000,000, very little perceptible detail can be preserved.
As the scale of a map increases, so may the level of geographic detail it
represents. Geographic features selected to appear on small-scale maps must be
exaggerated in size and simplified in shape so as to be recognizable by the map
user. These map generalization operations constitute an intriguing field of
research by cartographers attempting to formalize, and ultimately to automate,
the map creation process.
Reference
maps
Topographic maps record the
positions and elevations of physical characteristics of the landscape. They
serve as locational dictionaries for many endeavors, including environmental
planning, resource management, and recreation. The 1:24,000 scale United States
Geological Survey (USGS) series covers the continental
Fig. 1 Large-scale topographic mapping, percent
area coverage area at 1:1000 to 1:36,680 showing the uneven spatial distribution
of map coverage. (After United Nations, World Cartography, vol. 20,
1990)
Thematic
maps
Another problem with available maps
is that they often fail to include a feature of particular interest. Maps that
emphasize one or a few related geographic phenomena in the service of a specific
purpose are called thematic maps. An example is a thematic map that reveals the
uneven distribution of topographic map coverage around the world (Fig. 1).
Thematic maps are powerful alternatives to text, tables, and graphs for
visualizing potentially meaningful patterns in geographic information. Although
the production of large-scale topographic map series requires the resources of
large private or government agencies, individuals and small organizations with
access to relatively inexpensive personal computers, mapping software, and
databases can afford to produce thematic maps in support of business,
scientific, political, and creative endeavors.
Constructing geographic
information
Maps are composed of two kinds of
geographic information: attribute data and locational data. Attribute data are
quantitative or qualitative measures of characteristics of the landscape, such
as terrain elevation, land use, or population density. Locations of features on
the Earth's surface are specified by use of coordinate systems; among these, the
most common is the geographical coordinate system of latitudes and longitudes.
Geographical coordinates describe
positions on the spherical Earth. These must be transformed to positions on a
two-dimensional plane before they can be depicted on a printed sheet or a
computer screen. Hundreds of map projections—mathematical transformations
between spherical and planar coordinates—have been devised, but no map
projection can represent the spherical Earth in two dimensions without
distorting spatial relationships among features on Earth's surface in some way.
One specialized body of knowledge that cartographers bring to science is the
ability to specify map projections that preserve the subset of geometric
characteristics that are most important for particular mapping applications.
Prior to World War II, locational
data were compiled mainly by field surveys. Aerial surveillance techniques
developed for the war effort were then adapted for use in civilian mapmaking.
The scale distortions inherent in aerial photographs can be corrected by
photogrammetric methods, yielding planimetrically correct projections on which
all locations appear to be viewed simultaneously from directly above. Rectified
aerial photographs (orthophotos) can be used either as bases for topographic
mapping or directly as base maps.
See also: Aerial photography; Latitude and longitude; Photogrammetry
Influence of computing
technology
Periodically, cartographic practice
has been transformed by new technologies. Few have had such a profound effect as
the development of computer-based mapping techniques. While printed paper maps
still constitute the richest store of geographic information, cartography has
become as much a digital as a paper-based enterprise. With more and more
geographic data available in digital form, the computer has changed the very
idea of a map from a static caricature of the environment to a dynamic interface
for generating and testing hypotheses about complex environmental and social
processes.
Digital geographic
data
There are two major approaches to
encoding geographic data for computer processing. One, commonly called raster
encoding, involves sampling attribute values at some regular interval across the
landscape. Imagery scanned from Earth-observing satellites works this way,
recording surface reflectance values for grid cells (pixels) from 80 to 30 m
(250 to 100 ft) or less in resolution. Digital elevation models are matrices of
terrain elevations derived from satellite imagery or sampled from topographic
maps (Fig. 2).
Fig. 2 Computer rendering of the topography of
the 48 contiguous
A second method, known as vector
encoding, involves digitizing outlines of landscape features that are
homogeneous with regard to some attribute, such as a river, a watershed, a road,
or a state boundary. Vector encoding is more expensive than raster encoding, but
it is more flexible for many applications. One
Although the raster and vector
approaches for digital encoding predominate, these have been implemented in
dozens of idiosyncratic data formats designed to suit individual mapping
agencies and computer vendors. Incompatible formats have impeded data sharing
and have resulted in expensive redundancies in database construction. A
committee of
Constructing geographic
understanding
Geographic illiteracy is thought to
put afflicted societies at a disadvantage in an increasingly integrated
international economy. Access to geographic information is a necessary but
insufficient condition for constructing geographic understanding. Access to
analytical expertise is required to learn from the available information.
Geographic information
systems
Guiding much of the research and
development efforts of academic cartographers is the concept of automated
geography—an amalgam of computer databases and procedures by which analysts
might model, simulate, and ideally predict the behavior of physical and social
systems on the landscape. Concurrently, increasing social concern for
environmental protection stimulates a market for computerized geographic
information systems (GIS) that combine mapping capabilities with techniques in
quantitative spatial analysis. Many of the analytical procedures in these
systems—such as calculations of distances, areas, and volumes; of terrain
surface slope and aspect; defining buffer regions surrounding landscape
features; and generating maps of new features formed by the intersection of
several related map layers—have been codified by cartographers. Some
cartographers have investigated the potential of computerized expert systems
that may be used to assist nonspecialists in performing quantitative geographic
analyses. See also: Expert systems;
Geographic information systems
Cartographic
communication
With few exceptions, the outcomes of
analyses performed with geographic information systems are maps. Just as
careless or biased quantitative analyses result in erroneous conclusions, so can
unskilled map designs mislead users, and even the analysts themselves. Concern
for the integrity of thematic maps motivated cartography's largest research
project—the search for objective guidelines, based on psychological research, to
optimize map communication. Map design issues that have garnered the most
attention include classification techniques for grouping attribute data into
discernible map categories and logical systems for choosing appropriate graphic
symbols for representing different types of attribute data.
Interactive
cartography
Although many broadly applicable map
design principles have been established, the goal of specifying an optimal map
for a particular task is less compelling than it once was. Instead, there is
interest in the potential of providing map users with multiple, modifiable
representations via dynamic media such as CD-ROM, computer networks, and
interactive television. Even as computer graphics technologies and numerical
models provide ever more realistic environmental simulations, innovative, highly
abstract display methods are being developed and tested to help analysts
discover meaningful patterns in multivariate geographic data sets (Fig. 3).
Maps, graphs, diagrams, movies, text, and sound can be incorporated in
multimedia software applications that enable users to navigate through vast
electronic archives of geographic information. Interactive computer graphics are
eliminating the distinction between the mapmaker and the map user. Modern
cartography's challenge is to provide access to geographic information and to
cartographic expertise through well-designed user interfaces. See also: Land-use planning; Map design;
Map projections
David DiBiase
Fig. 3 Three geographic data variables related
in a scatterplot matrix and linked to a map. Locations of observations selected
in a scatterplot are automatically highlighted on the map. (From M. Monmonier,
Geographic brushing: Enhancing exploratory analysis of the scatterplot matrix,
Geog. Anal., 21(1):81–84, 1989)
Bibliography
G. L. Gaile and C. J. Willmott,
Geography in
J. Makower (ed.), The Map Catalog: Every
Kind of Map and Chart on Earth and Even Some Above It, 3d ed., 1992
P. C. Muehrcke, Map Use:
D. Wood, The Power of Maps, 1992
Ali
fazeli=egeology.blogfa.com
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