Friday, July 26, 2013
I
N D E X
1.
INTRODUCTION.
2.
FUNDAMENTAL STRUCTURE OF GIS.
3.
ATTRIBUTES OF GIS.
4.
AREAS OF GIS USAGE.
5.
THE GIS WORK STATION.
6.
DATA SOURCES FOR GIS.
7.
CONCLUSION.
GEOGRAPHICAL INFORMATION
SYSTEMS
INTRODUCTION :
A geographical
information system (GIS) is a computer–based tool for mapping and analyzing
things that exist and events that happen on earth. GIS technology integrates
common database operations such as query and
statistical analysis with
the unique visualization and geographic analysis
benefits offered by maps. These abilities
distinguish GIS from other
information systems and make
it valuable to a wide range of public and
private enterprises for
explaining events, predicting outcomes, and
planning
strategies.
DIGITAL REVOLUTION :
When
GIS first began to appear, users developed their own
Formats for storing spatial
information or employed those defined by vendorsand their proprietary software.
The formats were often specific to the
needs of particular projects and were not intended, initially, to meet the
needs of broder range of users. It was often very difficult to share and
transfer data. Users recognized that much time and money was being wasted when
datasets could not be shared among a broader clintele. At the federal level,
the United States Geographical Survey and the Bureau of the Census were among
the first agencies to begin experimenting with data formats that could serve
both their needs and those of a wider public.
The USGS’s digital line graphs (DLG) and the Census’s first
dual-independent map encoding (DIME) files were the result, although both of
these early formats have since been further relined into the DLG-2 and TIGER (Topographically Integrated Geographic
Encoding and Referencingsystem) formats. The DLGs were a way of coding
information drawn from the USGS’s conventional paper quadrangle sheet maps, the
DIME and TIGER Formats a method of encoding the maps needed for effective censers
tabulations.
As these standerds were being developed and used, the GIS world also saw a tremendous expansion in the range and
coverage of spatial datasets.
Large-scale digital map coverage was beginning to become
available
for entire states (such as
Texas) and cities (such as Austin). Many of these
were still kept in
proprietary software formats. Vendors and users,
recognizing the limitations
of being confined to these proprietary formats,
began to develop in the
1980s far more effective and versatile file transaction and conversion
software. This meant that data could be imported and exported between
proprietary software systems, some vendors, such as Auto desk, the makers of
the AutoCAD computer-assisted drafting
package, had tremendous success with their drawing exchange format (DXF), which
allowed easy transfer of spatial data among CAD-based GIS.
The development of standards and the proliferation of
conversion and
Translation software has had
a galvanizing effect on the GIS world. Where
Once users had to count on
digitizing datasets from scratch, they can now use a wide range of publicly
available files. The growth in available
files has been explosive and shows no sign of abating. The emergence of new
standards, such as the recently adopted federal Spatial Data Transfer Standard,
may even.
To create an address matching coverages, we needed to work
with the
AMF files initially found on
an IBM mainframe. Those files were ported to the workstation and C routines
were written to remove EBCDIC characters that had resided on the mainframe copy
of the files, FORTRAN routines were written to reformat the modified AMFs to
tiger format, so that the data
could be processed by the
workstation GIS to create an address matching coverage. The least expensive
Enumeration Area data we found had come prepared in the PC_GIS format, In order
to align it with the other geographics. We had to transfer it the workstation
(Unix) world. We exported the points in the PC package to DXF format and then
used network software to transfer the output from DOS to Unix format. Upon
returning to the workstation, we import facilities.
At this point all the data was finally resident in one
system – the workstation GIS. We used this environment align all geographics to
the same projection.
Then
we clipped the Address Match, Enumeration Area, Census Tract and FAS coverages
to ‘fit’ modeling boundaries, with these process done, all
that remained was to export the
workstation GIS data to the PC-GIS system.
Workstation coverages were converted to PC format using tools provided
by the PC-GIS vendor. The resultant files were then ported to the
PC-environment using the network utilities and ‘imported’ into the PC-GIS
product. We QA’d the data and then wrapped up the process by using the PC-GIS
to aggregate enumeration area data to census and FSA levels.
Increase the pace of development, in
beginning a GIS project, it is now wise to consider available digital sources
carefully to see what is available before plunging ahead with paper sources.
| DEFINITION : |
Geometric
information system are hardware and software systems
that provide for the creation, management,
analysis, and display of spatial
information.
Evolving from CAD packages, map display systems, and data
base and
spreadsheet software. GIS processes allow the user to perform
complex spatial
analysis difficult to achieve with any of the original systems that gave rise to GIS.
AVAILABILITY :
GIS software is available for a variety of platforms, from mainframes
to personal
computers . GIS procs range from a few
hundred dollars for
simple the matic
mapping packages to hundreds of thousands of dollars for
implementation
for cities with population in millions.
USERS :
Current users include private business
as well as local, departmental
and national
governmental agencies around the world. Applications include
facilities
management, natural resource inventory, land record maintenance,
and site
location analysis.
ATTRIBUTES OF
GIS :
GIS software packages use a variety of
approaches to the management of spatial
information, but most model information as paints and areas
with associated
attributes . While there are some successful raster-based GIS
products, most
are vector-based (with some capable of handling both).
Modeling in GIS application is often dependent on the
way in which a
specific GIS organizes
data. Database management techniques range form
simple
spreadsheets to complex data structures. Relational databases an
object-oriented
methods are very difficult in their internal structure, but both
methods have proven successful in
similar applications. One attribute of most GIS approaches is the use of a
common coordinate system to represent information. In many GIS implementations
real-world coordinates in the form of latitude and longitude are used, while in
others an arbitrary graphic unit is used. Some systems model height and some
can be configured to represent time as a fourth dimension. Data for GIS use
must be georeferenced, or registered with the common coordinate system, to be
useful. The accuracy of georeferencing has a significant impact on the validity
of the GIS packages can perform
geocoding, an operation that matches attribute data in one data base with similar attributes in a
georeferenced data base, resulting in
automatic georeferencing of the original database. The matching of
customer address in one data base with the georegerenced street and street
numbering representations in another database is a common use of geocoding.
DATA ACQUISITION:
Data
acquisition may be accomplished through the digitization of existing maps, keyboard
entry of attribute data, or by the importation of existing data files. Many GIS
packages allow for dynamic file sharing with data from spreadsheet or data base
management packages. Data storage and
management is an important task that may involve data transformations,
preprocessing, error checking, and the manipulation of mass storage devices. In
most vector-based systems, points or nodes represent geographic entities with a
single position in the common coordinate system. Utility poles, radio transmitters,
and customers addresses are examples of point entities. Points are also used to
represent those entities so small as to make their actual spatial extent
insignificant at the scale required for GIS analysis. Points are also commonly
used to represent area centroids, to arbitrary locate an entity such as a
label, or to position aggregate data within an area. Lines, polylines, arcs,
and spans are terms associated with groups of line segments that are used to
represent transportation routes, or other entities that link points within a
GIS database. Zones, polygons and regions are GIS terms for groups of lines
that enclose areas such as state boundaries, property lines, and soil type
delineations. Complex polygons may contain islands consisting of other polygons
or unmodeled areas.
Layers,
tables, overlays, and coverages represent ensembles of information related by
common attribute types. Layers are often thought of as similar to individual overhead
transparencies that can be stacked to show spatial relationships between them.
A layer containing soil-type regions can paired with a layer containing
vegetation zones for analysis and display by a GIS.
REQUIREMENT ANALYSIS:
GIS
analysis often requires many kinds of data manipulation. Most GIS packages allow
for statistical operations such as regression and correlation; mesurement
capability for distance, direction, area, and perimeter computation and geometric operations such as
rotation, translation, and scaling. Other capability may include functions written
in some other software language.
At
the heart of GIS modeling are geographic operators. A wide variety of operators
are available in different GIS packages for spatial analysis. Spatial operators
may include the ability to determine connectivity of line segments and the
relationships of those line segments to common attributes.
The
ability to determine topology is also an important capability found in more
sophisticated GIS packages.
Other
geographic operators commonly available in GIS packages are intersection, point
in polygon, area in area, and other expressions of interrelationships between
geographic entities that can be used to select, reject, merge, or query spatial
databases. Many GIS packages provide line thinning and smoothing operators.
Contouring and the graphic representation of three-dimensional surfaces are
desirable features. One of the most powerful geographic operations is the
creation of new entities from existing ones through proximity analysis.
Buffering is the creation of a polygon that represents the area within ten
kilometers of a hazardous materials transportation route is an example.
GIS
mapping capabilities often include the ability to handle different earth
shapes, geodetic datums, and map projections. These capabilities are required
by many users for the digitization of existing maps, and for the production of
useful output. The most useful GIS mapping systems support many different
scanners, digitizers, printers, and video output devices.
AREA OF GIS USAGE:
The
major challenges we face in the world today—overpopulation,
Pollution, deforestation, natural
disasters—have a critical geographic dimension. Whether siting a new business,
finding the best soil for growing bananas, or figuring out the best route for
an emergency vehicle, local problems, also have a geographical component GIS
component GIS will give you the power to create maps, integrate information,
visualize scenarios, solve complicated problems, present powerful ideas, and
develop effective solutions like never before.
GIS is a tool used by individuals and
organizations, schools, governments, and business seeking innovative ways to
solve their problems. Mapmaking and geographic analysis are not new, bur a GIS
performs these technology, only a few people had the skills necessary to use
geographic information to help with decision making and problem solving.
Today,
GIS is a multibillion-dollar industry employing hundreds of thousands of people
worldwide. GIS is taught in schools, colleges, and universities throughout the
world. Professionals in every field are increasingly aware of the advantages of
thinking and working geographically.
COMMON DIGITAL FORMATS:
The
way in which digital data is being made available is in flux. The first standard formats were
developed 20-30 years ago and still employed for some datasets. New formats are
also being developed. It is important for you to be aware of these formats
because they are so widely used.
·
Census Bureau Topographically
Integrated Geographic Encoding and Referencing System (TIGER) files or the
Tiger: Digital map database. TIGER files were developed to support the
tabulating function of the Census Bureau. Files for public use include digital
data for map features, boundaries, names, coordinates, and—for populous
areas—address ranges and zip codes. Coverage is for all of the United States,
including Puerto Rico and other territories of the U.S. They are grouped by state (or sets of
states), and by county (or sets of countries), and by statistical equivalents
in the territories. Census information is further broken down into census
tracts and block groups.
·
USGS Digital Line Graphs
(DLGs). DLGs are digital representations (by points, lines, and areas) of
cartographic information contained in the USGS’s traditional paper qudrangle
maps. Different kinds of data are arranged in layers. For instance: all hydrogrphic features contained
within a quadrangle will be provided in one layer (and so in one set of data),
and transportation information will be put into
another layer, and so on. DLGs come in various scales.
·
USGS digital Evaluation Models
(DEMs). DEMs are digital records of terrain elevations taken from the ground at
regularly spaced intervals. They are derived from the USGS’s quadrangle maps,
and are provided in various scales, Elevations are recorded every 30 meters for
7.5 minute DEMs, for instance.
·
USGS Digital Ortho photo
Quadrangles (DOQs) are aerial photographs, in digital format, in which the
relief displacement of ordinary aerial photographs has been removed so
that features are displayed in true
ground position. Information about DOQs can be found at the USGS’s Eros Data
Center.
·
Spatial Data Transfer Standard.
The SDTS provides a way for digital spatial information to exchanged from one
hardware system or software program to another.
COMMERCIAL
FORMATS:
Occasionally, software vendors develop
formats that become de-facto standards for the transfer of information. In the
world of GIS and cartography the most important of these is the dxf, or drawing
exchange format, developed by AutoDesk for the exchange of CAD files. The dxf
standards is an ASCII format that describes the contents of a CAD drawing in a
way that can be interpreted by other software systems provide a means of importing
and exporting dxf files in the AutoDesk format.
Often small problems arise in the
conversion of CAD drawings from and to dxf, but the format remains a very
effective way of transferring information. You should become acquainted with
the use of dxf because it is so widely employed.
THE GIS
WORKSTATION:
The
workstation GIS was used as the primary production vehicle, but the integration
process took on a decidedly electric flavor. Most of the geographies, including
the FSA and census boundaries, as well as MPSI’s proprietary modeling
boundaries were initially digitized on mini-computer drafting software (IGDS,
Intergraph Corporation, Huntsville, Alabama).
We
transferred these graphic files over to the workstation GIS format using
standard GIS import facilities. Corresponding attribute data was present in
flat files. This data was transferred into the workstation RDBMS (Oracle
Corporation, California) using the RDBMS vendor’s import facilities.
Once data was
in the RDBMS, we made the information more interpretable by manufacturing
additional attribute data, such as determining common business ratios and
various performance indicators. The attribute data was then transferred into
workstation GIS and joined with the graphics data using the workstation
system’s relational interface tools.
The net
result was a database, with all coverages cleanly lining up and attribute
information available at every level. The Integration was performed within 80
hours by two analysts. This database could not have been nearly as quickly (if
at all) if we had only used the PC GIS. The client was thoroughly impressed
that such a diverse set of information came together so quickly.
APPLICATION LAYER:
To
provide an easy interface to the user GIS is generally equipped with a very
good Graphical User Interface, which provides an easy and efficient interaction
to the user, This task is carried out by Application layer of workstation
of any GIS. The application layer should be provided with a good help
support for understanding the system very easily and the User should be
informed by appropriate messages so that he can understand the current
situation of the process.
It
is an interface to the data process layer which is very important for data
processing. The Application layer should
have a facility of taking input from the user
‘what to do’, It may be query or any graphical command.
DATA PROCESSING LAYER:
The
data processing layer receives input from Application layer as it ma be a query
or any graphical command. By following the requisite of the Application layer,
it searches data from the database and after processing the data it returns the
data to the Application layer as it’s requested format.
DATABASE:
The
database here contains a particular format it may contains data about
population of a region, areas available in that region, littermates in that
region, forests in that region or it may be the weather report of that region,
First we have to collect the data so that we can store it in the form of
database. So we have to find the data sources for our databases. There are
several data sources which can produce meaningful data for our GIS. They are as
followed.
DATA SOURCES FOR GIS:
GIS System Employ a Wide Range of Data
Sources
There
is tremendous range in the types of data used for GIS analysis. This reflects
the varied goals of the systems themselves. Since GIS may be used for
applications as varied as archeological analysis, marketing research, and urban
planning, the sources materials can be difficult to inventory and classify
comprehensively.
Even
within a single GIS project, the range of materials employed can be daunting.
CONVENTIONAL PUBLIC SOURCES:
In
some cases, you must still contact
providers in person or by mail to obtain data. And, as mentioned above. You may
have to do some detective work to locate public suppliers in your area. Do not
hesitate to make contact—most agencies are very helpful in providing
assistance. Useful contacts (these are by no means comprehensive) include:
·
The USGS. Data from the
Department of the Interior’s USGS may be acquired through Earth Science
Information Centers (ESICs).
(1-800-USA-MAPS). ESIC officers are scattered throughout the country.
·
The Census Bureau, which falls
under the juridiction of the Depatrment of Commerce. The Bureau provides an
array of demographic and socioeconomic data. Contact the Bureau of the Census,
Customer Services, Washington Plaza, Room 326, Washington, D.C., 20233,
Telephone: 301-763-4100 or fax:301-763-4794.
·
The U.S. Department of
Transportation, which provides information about the National Highway Planning
Network. Contact the National Ocean Service, NOAA, Riverdale. Maryland. 20737.
Telephone 301-436-6990.
·
For information about Texas, contact
the TNRIS at P.O.Box-13231. Austin, Texas, 78711-3231. Telephone 512-463-7847
or Fax 512-475-2053.
THE INTERNET AND WORLD WIDE WEB:
The
Internet and Worldwide Web are fast becoming a leading means of acquiring
primary and secondary data. In recent plans for the National Data
Infrastructure, the Internet is to become the primary means of disseminating
data produce by the federal government.
At the moment, finding exactly what you are looking for on the Internet can be
difficult, but navigation and focused searching of the networks are becoming
easier. Consider some of the materials that already available.
SOME OF DATA PROVIDERS FOR GIS:
·
The Geographer’s Craft’s own
index of data sources.
·
Internet GIS Information sites.
·
Manual of Federal Geographic
Data Products.
·
National Cartography and
Geospatial Center.
·
Fed World.
·
National Technical Information
service.
·
NASA.
·
National Environmental
Satellite, Data, and Information Service.
·
National Oceanographic Data
Center.
·
Library of Congress.
·
U.S. Dept. Commerce, State-USA.
COMMERCIAL SOURCES:
Many
software vendors earn a substantial income by repackaging and selling data in
the proprietary forms used by their software products. Because the data is
usually checked and corrected as it is repackaged, the use of these converted
datasets can save time. The widespread expansion of this marketing and
re-marketing of data has been a boon to many users who do not wish to be invest
resources in building the database they need on a day-to-day basis—they simply
buy what they need.
CONCLUSION:
GIS
is the only computer based tool for mapping
and analyzing the things that are happening on the earth. Think
geographically and make the world happy.
