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What is a GIS
GIS stands for Geographic Information
System.
GIS is the integration of spatial
(geographic) and a spatial (database) information into one
"system" that allows the user to interact with both aspects
simultaneously.
Spatial Data
Any
information about the location and shape of, and
relationships among features. This includes remotely sensed
data as well as map data.
It is important to understand that GIS is
a "system," not a specific software.
It is the most advanced electronic tool
for examining spatial information in an organized manner.
Every object present on the Earth can be
geo-referenced", is the fundamental key of associating any
database to GIS.
Input for GIS
The input for GIS can be obtained from
-
Survey of India (SoI) topographical maps
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Census data, scanned paper maps and
-
GPS (Global Positioning System)-derived data
-
Remote
sensing (RS) satellite Image
-
Aerial
photo
Depending on the kind of study and output required, the
type of input and analysis will vary. The power of GIS
lies in its integration capability between spatial
(geographical) and non-spatial or tabular data. Once
this relationship is established, any analysis can be
performed which will directly answer a set of questions
regarding real world problems.
A map is a graphic representation of some part of
the earth’s surface.
A map contains a series of themes or coverages that
are often combined to form the final product.
A map also contains descriptive information which
helps the reader interpret the information on the
map.
MapFeatures
Locational information is usually represented by
points
Lines
Polygons(Areas)
Point feature
A
point feature represents as single location. It defines
a map object too small to show as a line or area
feature. A special symbol of label usually depicts a
point location.
Line feature
A
line feature is a set of connected, ordered coordinates
representing the linear shape of a map object that may
be too narrow to display as an area such as a road or
feature with no width such as a contour line.
Area feature
An
area feature is a closed figure whose boundary encloses
a homogeneous area, such as a state Boundary, District
Boundary or Village Boundary.
picture
nPoint:
Discrete location
nLine
(Arcs):
Set
of ordered coordinates
nPolygon
(Area):
Closed
feature whose boundary encloses a homogeneous area
Map Characteristics
In
addition to feature locations and their attributes, the
other technical characteristics that define maps and
their use includes:
Map Scale
Map Accuracy
Map Extent and
Data Base Extent
To
show a portion of the Earth's surface on a map, the
scale must be sufficiently adjusted to cover the
objective. Map scale is expressed as a ratio. The unit
on the left indicates distance on the map and the number
on the right indicates distance on the ground. The
following three statements show the same scale.
1
inch = 2.000 feet => 1 inch = 24.000 inches => 1:24.000
The
latter is known as a representative fraction (RF)
because the amounts on either side of the colon are
equivalent: that is 1:24.000 means
1
inch equals 24.000 inches or
1
foot equals 24.000 feet
or
1 meter
equals 24.000 meters and so on.
Map scale indicates how much the given area has been
reduced. For the same size map, features on a small-scale
map (1:1,000,0000) will be smaller than those on a
large-scale map (1:1,200).
A map with less detail is said to be of a smaller scale
than one with more detail. Cartographers often divide
scales into three different categories.
Small-scale maps have scales smaller than 1 : 1,000,000
and are used for maps of wide areas where not much
detail is required.
Medium-scale maps have scales between 1 : 75,000 and 1 :
1,000,000.
Large-scale maps have scales larger than 1 : 75,000.
They are used in applications where detailed map
features are required.
So
each scale represents a different tradeoff.
With a
small-scale map, you'll be able to show a large area
without much detail.
On a
large-scale map, you'll be able to show a lot of detail
but not for a large area.
The
small-scale map can show a large area because it reduces
the area so much that the large-scale map can only show
a portion of one street, but in such detail that you can
see shapes of the houses.
GIS Links Spatial Data with Geographic Information About a
Particular Feature on a Map
The
information is stored as ‘attributes’ of the graphically
represented feature.
picture
Example: A line
that denotes a road tells you nothing but its location.
An attribute table stores all relevant
information about this feature, which can be queried and
displayed in a format based on the user’s needs
nFeatures
can be described by either a point or a polygon.
nSimilarly, lines can be of a specific width.
nMap scale and resolution define the conditions
for appropriate application of these feature types.
nSmall Scale - Larger Area
nHigh Scale – Smaller Area
GIS Significance
Listed
here are some examples which tell how GIS assumes
greater significance in understanding our basic
requirements
Which is
the best route between Hyderabad and Rajahmundry via
Vijayawada (a distance of over 400 km) having minimal
road intersection with good road and lesser traffic jam
during peak hours?
Which
part of Hyderabad has less literacy rate with unemployed
youth between 20 and 30 years of age?
Identify
the apartment houses in Hyderabad not following building
codes to withstand earthquake
GIS in business
A GIS is
a tool for managing business information of any kind
according to where it's located. You can keep track of
where customers are, site businesses, target marketing
campaigns, optimize sales territories, and model retail
spending patterns. A GIS gives you that extra advantage
to make you and your company more competitive and
successful.
GIS in agriculture
GIS is
used in a variety of agricultural applications such as
managing crop yields, monitoring crop rotation
techniques, and projecting soil loss for individual
farms or entire agricultural regions.
GIS in forestry
Today,
managing forests is becoming a more complex and
demanding challenge. With GIS, foresters can easily see
the forest as an ecosystem and manage it responsibly.
GIS in
transportation
GIS can
be used to help you manage transportation infrastructure
or help you manage your logistical problems. Whether
monitoring rail systems and road conditions or finding
the best way to deliver your goods or services, GIS can
help you.
GIS in
Site Planning
People
around the world use GIS to help them locate sites for
new facilities or locate alternate sites for existing
facilities.
GIS in
the military
Military
analysts and cartographers use GIS in a variety of
applications such as creating basemaps, assessing
terrain, and aiding in tactical decisions.
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