GIS Software, Mapping Software
and Geographic Information Systems
(GIS) Primer
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There are thousands of pages to explore in this site. GIS software
is simply mapping software. A "GIS" is a mapping software
program, most likely run in Windows in modern times.
GIS technology can be used for scientific investigations, resource management,
and development planning. For example, a Windows GIS might allow emergency planners to
easily calculate emergency response times in the event of a natural disaster, or
a GIS might be used to find wetlands that need protection from pollution. GIS
and mapping software play a central role in the geographic decision making of
cities, government, universities, military, environmental studies, and numerous
institutions world wide. Software for GIS, especially high value or free
software for GIS is of special importance. Manifold
System is a typical modern Windows GIS. Universities can get it virtually
free of charge, which was a key factor in its deployment. It can be used
with more of the GIS data links and other GIS and mapping information on the Web
than almost any other Windows GIS or mapping software at any price for
any system.
What is a GIS? How is it used
for maps and mapping?
In the strictest sense, a GIS program is a
computer application capable of assembling, storing, manipulating, and displaying
geographically referenced information , i.e. data identified according to their
locations. It's like a mapping software package combined with a database plus
analytics. Practitioners also regard the total GIS software or mapping software
solution as including operating
personnel and the data that go into the system. GIS has come a long way in the
last two years. If your mapping software or GIS is older than two years
old, it is quite likely obsolete. Old fashioned GIS's are slow and
expensive. Modern GIS packages cost less than two hundred dollars and
provide more performance than older systems. Mapping software is now very
high performance and inexpensive. Free GIS software of various kinds has
become available, although it is usually a viewer tied to a much more expensive
package. More importantly, there are numerous Government sources of free
maps. Free GIS maps are the best kind.Relating information from
different sources in GIS
If you could relate information
about the rainfall of your State to maps of your county (free maps,
ideally) using mapping software, you might be able to
tell which wetlands dry up at certain times of the year. A GIS, which can use
information from many different sources, in many different forms can help with
such analyses. The primary requirement for the GIS source data is that the locations
for the variables are known. Location may be annotated by x,y, and z coordinates
of longitude, latitude, and elevation, or by such systems as ZIP codes or
highway mile markers. Any variable that can be located spatially can be fed into
a GIS. Several computer data bases that can be directly entered into a GIS are
being produced by Federal agencies and private firms. Different kinds of data in
map form can be entered into a GIS. Integrating complex database
information in a visual map interface is what sets a GIS apart from
ordinary mapping software.
A GIS can also convert existing
digital information, which may not yet be in map form, into forms it can
recognize and use. For example, digital satellite images can be analyzed to
produce a map like layer of digital information about vegetative covers.
With Manifold System, rasterizing packages are used to convert scanned paper
maps into digital maps. An excellent free package for converting scanned
paper maps into digital maps is distributed by (of all people!) the United
Nations mapping authority. Likewise, census or hydrologic tabular data can
be converted to map-like form, serving as layers of thematic information in a
GIS. Database products such as Database Commander are key products for
manipulating and transforming databases for GIS use that might be fetched from
government or private web sites.
Data Capture for GIS
How can a GIS use the information in
a map? If the data to be used are not already in digital form, that is, in a
form the computer can recognize, various techniques can capture the
information.Maps can be digitized, or hand-traced with at computer mouse, to
collect the coordinates of features. Electronic scanning devices will also
convert map lines and points to digits. This is such a time
consuming operation that almost all GIS users employ digital maps created by
government agencies such as the USGS. A modern GIS like Manifold will
support government digital map formats such as DLG, VPF, SDTS, TIGER/Line, DEM,
gtopo30, GLOBE, and others so you can easily download maps from the hundreds of
government sites that provide them for free.
A GIS can be used to emphasize
the spatial relationships among the objects being mapped. While a computer-aided
mapping system may represent a road simply as a line, a GIS may also recognize
that road as the border between wetland and urban development, or as the link
between Main Street and Blueberry Lane.
Data capture - putting the
information into the system - is the time-consuming component of GIS work.
Identities of the objects on the map must be specified, as well as their spatial
relationships. Editing of information that is automatically captured can also be
difficult. Electronic scanners record blemishes on a map just as faithfully as
they record the map features. For example, a fleck of dirt might connect two
lines that should not be connected. Extraneous data must be edited, or removed
from the digital data file. To avoid this time consuming process, use
Manifold and download free government maps.
Data integration in GIS and
Mapping
A GIS makes it possible to link, or
integrate, information that is difficult to associate through any other means.
Thus, a GIS can use combinations of mapped variables to build and analyze new
variables. Using GIS technology and water company billing information, it
is possible to simulate the discharge of materials in the septic systems in a
neighborhood upstream from a wetland. The bills show how much water is used at
each address. The amount of water a customer uses will roughly predict the
amount of material that will be discharged into the septic systems, so that
areas of heavy septic discharge can be located using a GIS.
Projection and registration
in maps
A property ownership map might be at
a different scale from a soils map. Map information in a GIS must be manipulated
so that it registers, or fits, with information gathered from other maps. Before
the digital data can be analyzed, they may have to undergo other manipulations -
projection conversions, for example - that integrate them into a GIS.
Projection is a fundamental
component of mapmaking. A projection is a mathematical means of transferring
information from the Earth's three-dimensional curved surface to a
two-dimensional medium - paper or a computer screen. Different projections are
used for different types of maps because each projection is particularly
appropriate to certain uses. For example, a projection that accurately
represents the shapes of the continents will distort their relative sizes.
Since much of the information in
a GIS comes from existing maps, a GIS uses the processing power of the computer
to transform digital information, gathered from sources with different
projections to a common projection.
Data structures and Database
usage in GIS and Mapping
Can a property ownership map be
related to a satellite image, a timely indicator of land uses? Yes, but since
digital data are collected and stored in various ways, the two data sources may
not be entirely compatible. So a GIS must be able to convert data from one
structure to another.
Image data from a satellite that
has been interpreted by a computer to produce a land use map can be "read
into" the GIS in raster format. Raster data files consist of rows of
uniform cells coded according to data values. An example would be land cover
classification.
Raster data files can be
manipulated quickly by the computer, but they are often less detailed an may be
less visually appealing than vector data files, which can approximate the
appearance of more traditional hand-drafted maps. Vector digital data have been
captured as points, lines ( a series of point coordinates), or areas (shapes
bounded by lines). An example of data typically held in a vector file would be
the property boundaries for a housing subdivision.
Data restructuring can be
performed by a GIS to convert data into different formats. For example, a GIS
may be used to convert a satellite image map to a vector structure by generating
lines around all cells with the same classification, while determining the cell
spatial relationships, such as adjacency or inclusion. Thus a GIS can be used to
analyze land use information in conjunction with property ownership information.
Data modeling
It is difficult to relate wetlands
maps to rainfall amounts recorded at different points such as airports,
television stations, and high schools. A GIS, however, can be used to depict
two- and three-dimensional characteristics of the Earth's surface, subsurface,
and atmosphere from information points.
For example, a GIS can quickly
generate a map with lines that indicate rainfall amounts. Such a map can be
thought of as a rainfall contour map. Many sophisticated methods can estimate
the characteristics of surfaces from a limited number of point measurements. A
two-dimensional contour map created from the surface modeling of rainfall point
measurements may be overlain and analyzed with any other map in a GIS covering
the same area.
Information retrieval
What do you know about the swampy
area at the end of your street? With a GIS you can "point" at a
location, object, or area on the screen and retrieve recorded information about
it from off-screen files, topo maps or other sources.
Using digital maps originally
created from scanned aerial photographs (by USGS or similar creators of digital
maps) as a visual guide, you can ask a GIS about the geology or hydrology of the area
or even about how close a swamp is to end of a street. This kind of analytic
function allows you to draw conclusions about the swamp's environmental
sensitivity.
Topological modeling
In the past 35 years, were there any
gas stations or factories operating next to the swamp? any within two miles and
uphill from the swamp? A GIS can recognize and analyze the spatial relationships
among mapped phenomena. Conditions of adjacency (what is next to what),
containment (what is enclosed by what), and proximity (how close something is to
something else ) can be determined with a GIS.
Networks and GIS and Mapping
If all the factories near a wetland
were accidentally to release chemicals into the river at the same time, how long
would it take for a damaging amount of pollutant to enter the wetland reserve? A
GIS can simulate the route of materials along a linear network. It is possible
to assign values such as direction and speed to the digital stream and
"move" the contaminants through the stream system.
Data output in GIS and
Mapping - Creating new maps
A critical component of a GIS is its
ability to produce graphics on the screen or on paper that convey the results of
analysis to the people who make decisions about resources. Wall maps and other
graphics can be generated, allowing the viewer to visualize and thereby
understand the results of analyses or simulations of potential events.
